What kind of songwriting are we talking? Are we talking lyrics, composition, or both? Steve Vai calls himself a songwriter, I call him a brilliant composer, and a terrible songwriter.
Perosnally, I make my living as a singer/songwriter. I am no composer, my music is fairly simple, more just a vehicle for lyrics, than actual composition. I guess my question is, are you asking for advice on being a lyricist, or a composer/arranger, or a little of both. I can help alot with the lyricist part, and have taught at workshops and such. The other I ain't so great at...
Jake
P.S.- for my own stuff, I kind of tend to throw rules out the window, and write whatever I feel like. They ain't hits, but I've sold enough records to think they must be decent songs. If you want to hear a few, you can check out my myspace:
www.myspace.com/gsharper