capitalalchemy is right - A passion and feeling for what you are writing about is just as important, if not more important, than being a theory whiz. I read an interview with Don Henley recently, and his advice to beginning musicians/songwriters was this: "Read books, read poetry, listen to songs of great writers. Being able to play and knowing theory is great, but there a hell of a lot more good players than there are lyricists." Find a subject that means a lot to you, and decide how you feel about it. By playing around with a just a couple scales, you can make your guitar talk in ways that you never even could with your voice. Also, play with string bends, hammer-ons, pull-offs, etc. They add a lot of character. You'll be fine.