Get a mac.  Everything sounds better on a mac. 

1. The pint glass method. Find an empty one that tapers in towards the base, and place your handset into it speaker-end first. This will create an echo chamber that amplifies the sound. 

Listen to David Hasslehoff's records for several hours, then play back your track directly afterwards.
You will notice a significant improvement. This technique is known as "ear training".

Thanks for all the tips! They all sound too hard though. It's way easier to just complain about it and then blame my lack of success on Sonar. See, I suddenly had this thought. What if I listen to David Hasselhoff, transpose to A minor, put it on a Mac, select the right setting for my song, and it STILL sounds like crap!!!? THEN who can I blame? 
 
No, better to just tell people if they don't like it to blame Sonar.

 
This what you're looking for?

Research has proven that "louder sounds better" to most people.  The "make it sound better" slider is right in front of your face, although using it is a bit counter intuitive.   Insert the Concrete Limiter in the master bus and make sure it's POST fader.   Then slide the the input slider DOWN, D-O-W-N, to raise the volume of your entire song.   Keep sliding until you love the way it sounds.
 
I know!  You're slapping your own forehead right now for not realizing it earlier!  
 
For selecting clips across tracks, use "Process-Gain" and add the needed volume destructively.
 
"Turd Polishing" has been discussed exhaustively in this forum (as well as in others).  Try searching "polishing a turd" for more suggestions.
 
Best of luck!!!

> Try searching "polishing a turd" for more suggestions.
 
And please remember that the 64 bit turd polishing engine should be switched on at all times as it is a proven fact the turds comes out nicer that way, especially when downsized or dithered (make sure your drains are unblocked).......
 
For full evidence please refer to this equation/dump .....
 
To Mega Therion ([Hebrew] THRIVN): The Beast 666; MAGUS 9^○=2^□ A∴ A∴ who is The Word of the Aeon THELEMA; whose name is called V.V.V.V.V. 8^○=3^□ A∴ A∴ in the City of the Pyramids; OU MH 7^○=4^□ A∴ A∴; OL SONUF VAORESAGI 6^○=5^□, and ... ... 5^○=6^□ A∴ A∴ in the Mountain of Abiegnus: but FRATER PERDURABO in the Outer Order or the A∴ A∴ and in the World of men upon the Earth, Aleister Crowley of Trinity College, Cambridge.
 
Thankyou...

To make it sound better. Practice, practice and more practice! 

Get some noise-cancelling headphones.  What's left is the good stuff, like the center of a Tootsie Pop.
 
Bob Bone
 

Play the piano backwards.  That works for me.  I do everything backwards.  Backwards is forward if you get turned around.  And forget what Fuddyduddy said.  Get really high.  Really really high.  Get knocking-over-micstands high.  Drink 12 Southern Tier IPA beers that have 7.5% alcohol.   Go from there.  There are 5 stages of "High" - go for number 5.  Everything will sound GREAT!!   In case you don't know them, here they are: 
 
1. Social - interfacing with others is improved, inhibitions reduced, you believe you are attactive to potential lovers
 
2. Buzzed - still 'social' but now you have to worry about the man in the blue suit and his flashy light 
 
3. Hammered - social is bye-bye, some people feel sorry for you, you stumble about, you concoct ludicrous sentences and tell tales that make no sense, you spill your drink, you fall down some stairs
 
4. Blotto - OK now you are all sweaty, and have that white crap at the corner of your mouth, you spill other peoples drinks, you just puked and you want to make out
 
5. Spectacle - your on Youtube, groups of strangers want to beat you up, your bandmates do beat you up when you fall off the stage and break your guitar getting the band fired, you have a handcuff on one wrist, your car door is gone for some unknown reason, you make out with your wife's sister, you jump in bed like superman trying to be romantic and you bounce off the bed smashing your face into the end table opening a huge blood-pouring gash above your eye, you still want to make out.