Common endpoint when recording without a real song plan before hand:
- Have recorded a nice drum part
- Have laid down a nice complex chord progression on electric guitar
= Can't go anywhere!
 
Project ends up gathering dust on my HDD for years. Maybe it's a bridge part for a song I haven't written yet?

More often than not?   Slowly.
 

I start and then always get hung up on drums - which then kills the entire thing

My approach begins with a hook. It is usually a phrase. That phrase will have a rhythm to it that will dictate where it's placement in the song should be.
Longer phrases lend themselves to the last line of the A verses in an AABA format. Shorter phrases work really well in the first line in B choruses of ABABCB.
The rhythm of the hook will also point the way to the feel and tempo of the song as do the subject of the hook.
Before I even power up Sonar, I grab a piece of paper and my Martin D28 and figure what kind of song I want to come up with. I work with a lot of co-writers
in Nashville and we will write with specific pitches in mind. Once I have the skeletal parts of the song feeling good I'll record myself singing into my iPhone, type up my
lyric and subject matter ideas and send them to co-writers who add to the song foundation. Once we agree on the feel, song structure and tempo, I'll open a new session in Sonar.

Now comes the recording of the work tape.

I begin by setting the tempo and recording a reference track with me singing with my guitar to track one and place markers.
Becoming more familiar with the song allows me to program a scratch drum track either using a simple loop or sequencing a bare bones drum track using either Session Drummer or
Addictive Drums.
I'll then lay down a bass track direct by going into a Radial JDI into a Black Lion B173 into a Ashly SC50 into a Motu 896mk3 into Sonar.
After that I'll further tweak the drum/loop tracks to create a better dynamic flow.
Acoustic guitars come next. Often I'll record a D28 with an LR Baggs into a Fishman Aura into the B173 for panning hard left.
Then a different guitar, usually a Martin 0018 in open G or Nashville C drunk tuning will be recorded with a Shure P81 into the B173 and Ashly and panned hard right or vice versa.
Next is the work tape vocal recorded with a Shure KSM32 into the B173 and Ashly and tuned up in the stand alone Melodyne.
I'll export that session with an SSL bus compressor and Waves L2 on the master fader to bring the level up and create an mp3 to send to my co-writers.
I save that session (and all sessions) to a bundle and redundantly save to a internal solid state drive, an external HD and Dropbox.
Feedback is gathered, tweaks are made, publisher input, more tweaks and then the demo phase begins and comes down to a matter of putting the right
instruments in the right places to support the song and the vocals.

As I demo, 99% of the time I will create the backing tracks and hire a Nashville vocalist to sing the demo with harmonies with me producing via Skype from my studio.
 
My 'finished' demos are usually:
Hired male or female vocalist
Live drums to replace or play with my programming
My acoustic guitars and bass
Hired session guitar and keys if needed.
 
I import those files into my Sonar session and mix using Waves, ProChannel stuff, SoundToys, Slate plugs and cool freeware I picked up along the way, master and deliver.
 
For me Sonar is both a drawing pad and a program to deliver mastered content.

It all begins from a feeling that I could write something new. I grab my bass, guitar or play with Hammond or piano to improvise for a while. Usually some melody starts to get more attention in my head and it will become the seed of the new song.
 
Now things are evolving fast. I make the chord progression in minutes and make a quick demo in SONAR. First track may is usually bass or rhythm guitar. I don’t need to make any drum track – I’m used to play over the ¼ metronome.
 
After making a rough structure of the song I play electric demo drums - usually some real drumkit setu from Native Instruments Ultimate library -  and pay more attention to the groove. Now I play all instruments again 1-3 times. Each time I learn more about the song and finally I know exactly what all instruments are doing (and WHY). Mixing process has already started – it’s integral part of the arrangement and sound choices.
 
It’s time for the vocals. Demo vocals are recorded quickly but refining continues all the time to the last minute before mixing.
 
Now the professional drummer comes to studio. I give him the song structure, play the demo for a couple of times and he makes his own markings. Drums are recorded in 1-5 takes and in two hours I have got superb drum track (no editing required), including sound check and rough drum mix. I have learned that it is cheaper and faster to hire a seasoned professional than trying to make drums on my own.
 
Drums are ready. Next I play bass and guitar again and make them groove with drums. Vocals, keyboards, synth programming, rough mixing, backing vocals etc. follow in random order.
 
Mixing phase: sometimes I tend to use “advanced mixing techniques” which means that I could re-record any instrument track or even lead vocals if I have a feeling that song does not feel right. “Song is ready when it is ready”. Normally, however, mixing is just mixing.
 
Finally it’s time to send song for the mastering engineer. It’s good to have a deadline; otherwise the mix would not become ready until year 2080…
 

My process has not changed for years, and has worked out well for me.
 
The process begins with acoustic guitar.  I begin to flesh out ideas.
 
As soon as I have decided on a basic chord pattern, I create a song in Band-In-A-Box.  I enter the chords and choose a style that comes close to what I am hearing in my head.  I stay with acoustic guitar and BIAB, making chord changes and adjustments until I have the song essentially complete.
 
If I decide that the song is worthy of making a demo, I move the BIAB files to Sonar.  
 
I record a guide vocal track.
 
Then I start replacing the BIAB tracks with my own recording.  Sometimes, but seldom, a BIAB track actually makes it to the final mix (the BIAB Realband acoustic guitar tracks are often quite nice).
 
I replace the guide vocal track with the keeper vocal track, then add additional vocals (harmony, back-up).
 
Re-do and/or tweak as necessary.
 
One advantage of using the BIAB tracks is that it allows me to record my own tracks along with "the band."  For example, if I am recording a guitar track, I am playing along with a full-band arrangement of the song, and not just a click track or a drum loop.  I find this process to be quite satisfying.
 
Another advantage is that listening to and singing along with the BIAB tracks allows me to make smart tempo decisions early in the process.
 

SvenArne
Anything I ever came up with that didn't start with a sung melody always turned out stupid. Sometimes amusingly so, though...

 
I'm a melody person as well.

 
This is such an AWESOME question, Craig... and the diversity of answers is amazing...  A man of many words said a lot in just a few:
 

bapu
For me it all starts with words.
 
Don't need SONAR for that.

 
I agree! Often I start outside of the studio/DAW land... a lot of what I do stems from focusing on an issue... sometimes a podcast dealing with a particular climate situation or solar/technology thing, a twitter link or study or ... I'll be driving and listening to some sciency thing and finally pull off the road, wip out Evernote, and start writing, REAL TIME, while listening.  Hook lines, many are there in what people say... and I've been swept away into a writing frinzy more times than I can count...listening to an amazing human discussing something that I feel is crucial to understand.
 
I have 20 or so themes active at any time.  Actually, this number continues to grow... As a vocalist I'll then reflect on a subject matter and how I emotionally react to an issue and bring up some rhythmic/arp/multi package(s) that  seem to fit the picture I'm feeling, and then just vamp... often with words on a separate monitor, Often with a drum underpinning that I just select from the endless pile I have, always with headphones, mic on and... away I go.  I may do this with a variety of starting points, and may vamp on several possibilities before I start to flush things out for a word package... Of course, I sometimes just fire up a new instrument or "package", like the Guru's new Kreaturesque package... and just start there, with absolutely NO idea of what I'm gonna do... That is just as fun and the spontaneous combustion which results is often a reward in itself... When Airwave and Skippy came out with their O2 masterpiece I spent ALL NIGHT writing... totally extemporaneousa but powerful songs, singing/playing real time, not knowing where it would go next, moved by the multi itself... a dozen songs, several very good, in an all night "holy SHEEEET" session... I love a number of those moments, like "are we a virus" which TOTALLY flowed from the power of others gifted into my hands and daw...
 
My mood or state of mind generally moves me in a direction... whether emo, country, new age, rock, orchestral, angry screaching or plantively calling out or whatever... I'm never in a box...well, I AM in the box of saying something that needs sayingt...  Indeed, sometimes I'll just fire up a vst...an OT guitar, an Albion patch, or guru Omnisphere multi... and let the muse take hold.  Often with NO predetermined melody... even though I feel melody and hooks are key to a song that communicates.
 
I go thru phases... on my last camping trip, armed with just my acoustic guitar and a smart phone, I vamped dozens of ideas I would NEVER have come to in my studio setting...words, riffs, rhythmic foundations... I was like, "WTF!!! where'd this come from???" Being able to live capture these days is HUGE.... I remember the day when I had to concoct my own system to remember an idea, before the digital age.  We are SOOOOOO lucky at this moment in time to have the tools we have.
 
Like my gardens, I feel songwriting is an artistic adventure and I try to avoid rules for what first flows.  Sure, after I come up with something that excites or brings tears to my spirit, I'll do the tear down, edits, and redos/harmonies/overlays... the boring but necessary piano roll tweaks...
 
But mostly, it's art... and it is soooo amazing to be able to wield someone like Airwave's art as a foundation for my own unique feelings and perspectives...It's like being IN a band without dealing with the challenges of BEING in A BAND!  Every patch library is a creation lovingly put together by another human... and THAT sound, which I WOULD NEVER find on my own, rocks me into directions I NEVER anticipated...
 
I own ALL the costly tools but rarely use them, due to lack of time and general overload. I don't redo as often as I should.  Indeed, part of why I'm relocating up north is to have way more time to devote to honing my often crude emotional appeals... Excited to see where THAT leads.

Another BIAB user here.
 
Usually I work out the chord sequence (and lyrics) with a guitar, then the structure of the song in BIAB (if the song sounds good there, it might sound decent elsewhere, too ). Then I export the song to midi and import it to Sonar.
 
I usually end up using the BIAB drum track and a one or two other tracks, assigned to completely different (sampled) instruments the BIAB style makers intended (that’s why I hate all the RealTracks). After I have groove quantized, edited, transposed, cut and pasted to my hearts content and probably added a couple of (looped) African/Middle Eastern percussion tracks, I bounce the midi/sampler/synth tracks to audio tracks. (The drum track gets broken apart as several audio tracks: snare, toms, cymbals, kick drum and kick drum doubled with a synth kick drum sound for extra oomph.) Some of the other (originally midi) tracks serve mainly as guides, some are supposed to survive until the mix.

Then I add a couple of guitars, bass and vocal tracks, not necessarily in that order. Then mix. Then take a break and later on listen to what I have with my iPod and/or with the home stereo. Re-record and re-mix if necessary (as it usually is). Go back to the beginning a few times and start the song anew with a different tempo, different rhythm, different instrumentation, whatever...

 
I have a project template with AD2, two guitar tracks, a bass track, two for keys, and three for vocals. This is my basic working setup.
Inspiration can come from anywhere; noodling on guitar, hearing something on the TV or radio, something I read, or even a random thing I think or someone might say.
If it's an idea from playing guitar (my main instrument), I might immediately record the basics of it just so I don't lose it. Then I find a suitable basic beat in AD2 and layout enough of it to get me started (usually about 100 measures). I work on the chords and arrangement, including choruses and bridges as applicable, over this basic beat.
When I have the arrangement I record a scratch rhythm guitar track. This might be a keeper or might not even be included in the finished song. Then I do the bass track. When I track these parts I almost never comp, I'd rather do an entire track in one complete take. To me this lends more of an "organic" feel to it, or at least as much of that feel as you can get when you're doing most of the tracks yourself with computerized drums. If it's a particularly difficult part, especially on bass, then I will comp it.
Simple keyboard parts I do myself, but anything more than just block chords is way beyond my skill set. If I can make it work I'll use EZ Keys, it's an amazing program with enough midi loops to cover just about any basic (and some not-so-basic) songs. Luckily I have a couple of friends who are great keyboardists that are willing to help me out if EZ Keys won't work. I send them a basic mix of the arrangement and they record their parts into a midi file which they send back to me to use in the final mix. That way I can use whatever instrument I have that will work in the song.
If I haven't written the lyrics by now I'll record a scratch vocal track with random words or nonsense syllables, sometimes not even melodically, just searching for the right cadence to work with the music.
After the vocals go down then I'll do the ear candy; BG vox, guitar solos, percussion, etc.
Then I get to the REAL fun, mixing it all down and gluing it together. I think I actually enjoy that part of it the most, the pressure to try to create something worthwhile is mostly gone, it's just a matter of getting it to sound as good as possible.
That's the usual basic process, but of course there are times when it's completely different.
Sorry for the long post, I get a bit carried away.....
 

Here's an example of a song I recently wrote.
Noodling away on a guitar while watching TV, I came up with cool lick.  After playing it a few times, I built a basic chord progression around it and sang a verse (whatever words came to mind).  Opened Sonar, and recorded my playing the chord progression, lick, and sang the verse.
Then I threw together a simple drum beat that felt close, and added a simple bass line.  Then I wrote a chorus, 2nd and 3rd verse, and recorded them.  That became the basic "so I don't forget" recording.
Then I got off the PC and went back to the guitar to re-arrange the song, add a middle-8 section, whatever felt right as a performance.  Then I went back into the Sonar project and updated it with whatever else came out.  Export a copy so I can listen to it on my phone as I do other non-musical things.
At this point, it was a fairly run-of-the-mill blues song.
A week or so later, I was listening and imagined another guitar line working as a counter-melody.  Since I felt the song wanted some brass, I programmed a 2-trumpet/1-trombone section.  Then this re-inspired the other instruments and I rewrote the bassline and drums to match how the feel changed.  Somehow this led my blues song into a weird Klezmer field.
I didn't want it to be a Klezmer song, so I replayed the brass on a guitar.  Then it leaned a little more back towards blues-rock.  I exported an updated version of the song.
A week or so later, I was working on something in the song and isolated one of the guitars.  Suddenly i thought "i wonder how this would work as reggae?"  A quick drag/drop of a reggae drum pattern, a "wing-it" bassline, and there was another life of this song.
 
Now I'm leaning back towards the blues-rock version.  But it will likely involve a little reggae/klezmer by the time I finally complete a mix I'm proud of.
 
Most of my songs evolve like this.  There usually ends up being 3 or 4 versions of each.  Occasionally I'll have the songs transform between genres gradually, but sometimes they just live in different worlds.
 
I used to be a fan of Hawksley Workman, and what impressed me most was that you rarely saw him play the same set twice.  if he was in a hard-rock mood, you got a hard-rock show.  If he was feeling ballady, you'd get a softer, more sedate concert.  And his songwriting and arranging were good enough that the songs worked in whatever genre he chose.