I'm looking for an easy way to keep levels consistent between different tracks/sources and not clipping during recording and mixing. My levels have always been inconsistent, particularly audio vs synth tracks.  Any ideas would be appreciated.

I've found it pretty useful to track (or gain stage existing tracks if you aren't recording them yourself) in the -18db to -15db range. Stealing this from David Glenn (who might've stolen it from someone else), but if you shoot for kick, snare, bass & lead vox to sit in the -15db range with everything else around -18db, that should give you a decent starting point for a static mix. (Keep in mind that some tracks are going to have a much higher dynamic range than others so it's not the -15/-18 trick is a guaranteed workflow...just a good starting point.)
 
I've found that even with a really high track count I still have plenty of headroom and I'm not overloading plugins, which I've heard is important for plugins modeled on analog gear because they're expecting a signal around 0VU which is much lower than 0dbfs in the digital realm.
 
In regards to soft synths, you'll most likely have to tone down the output from the synth itself to keep it in line. Most of the synths I use output at a really high level so I almost always turn down the output so it's hitting the track in that -15 to -18 range.

@streckfus - I follow the same approach myself, including generally starting with a downward adjustment at the soft-synth instrument level, and then using Sonar track gain knobs for a finer tuning, to get things to approximately -18 dB, as well.
 
Additionally, whenever I set up a new track template for a given drum kit in Battery 3, since these always include each kit piece having its own audio output channels from Battery 3, I also adjust each kit piece's audio track to set the level to a starting point between -18 and -15 dB, so that when I later include that kit into one or more future projects, all the tracks are already set to my target levels.  This saves me loads of time.
 
I gave a silent 'Wahoo!' as a read your post :)
 
Bob Bone
 

Thanks for the responses.  I tried setting up a track and I discovered that the input gain control is not working.  I can turn it all the way up or down and there's no difference.  What am I doing wrong?

I'm not in front of SONAR right now, but I'm pretty sure if you're trying to adjust the gain on a soft synth track, nothing is going to happen. If it is a synth track, I'd open up the synth itself and look for the output knob on the synth, then adjust that until the track meter is hitting your desired level. 
 
 

I never touch the gain or faders for midi tracks - anytime I am speaking of adjusting gain or faders, it is ALWAYS referring to the associated audio tracks.
 
So for ME, I would firstly look at how hot the output volume is set for a given loaded soft synth instrument(s), and then would fine tune the gain for that instrument's associated audio track(s), leaving the midi faders completely alone, and only adjusting the audio track gain for the instrument - to get to the -18 dB that I have chosen as my initial starting point prior to recording anything.  So, for MY projects - everything should be producing audio at or near -18 dB, with all audio and midi faders at Unity.
 
I hope I the above is a clearer explanation of anything I posted earlier. :)
 
Bob Bone

streckfus
I've found it pretty useful to track (or gain stage existing tracks if you aren't recording them yourself) in the -18db to -15db range. 

peak or rms?

Sorry, I forgot to mention it's an audio track.

well, you basically need *rider* plugin,
I created a dedicated ideas&requests forum thread for it days ago:
http://forum.cakewalk.com...-leveler-m3445219.aspx

I wish there was some magic secret to doing this, but there is not.
there just many ideas, theory but most important...rules to go by.
 
don't be afraid to push it..don't distort it, but don't be afraid to push it.
especially in hard rock music, I find a grainy more attitude approach works better than having a delicate sweep of all levels within ranges. the only thing you need to concern yourself with is that the master volume is not blowing up.
I mix any where from -3dB to -7dB. I get my thrashing levels in a master not a mix.
 
I use automation, a lot of it.
I use compressors, a lot of them. (don't over do it with compression)
hand limit those peaks that slam the compressor by automating gain.
 
but the most important advise I can give you or anyone else for that matter is to experiment.
try different thing, write down certain things you wont remember later.
Watch you tube videos (just make sure your watching someone who knows what they are talking about)
ive seen some good ones.