Man, this is all really good advice! I think I'll try making a song with each tip to see what works for me, and hopefully kill some old habits. I was also reading The Complete Idiot's Guide To Music Composition today, and it had a section that I thought was really cool. It said that instead of doing A parts and B parts, maybe think of entire sections of the song as A parts and B parts, with their own patterns (like ABAB) inside them.
I'm working on a song right now that goes:
ABC ABC
DEF DEF
CBA CBA
DEF DEF
AA
So the "A" section is ABC, and the "B" section is DEF. But I made it so that A and D are variations of each other, as are C and F. So when DEF goes into CBA, the F and C flow like one piece. And then when it goes out of CBA back to DEF, the A and the D flow together.
I don't know when that track will be finished, but the pattern's working really well, so I wanted to share.
Once again, thanks for all the help so far! It's really appreciated.