Not that I'm a great songwriter or anything but the actual lyrics themselves aren't that important it's the vocal line that has to be really good.( e.g.I am the walrus by the Beatles nobody knows what that ****'s about but Lennon/McCartney are generally recognised as the best ever songwriters)

I've figured out some good vocal lines by jamming over the chord progression Im using. However, if you've got a singer in your band worth his salt you won't need to do this.