Obvious rhymes, like shoes with blues, should be avoided as much as possible, but don't let any artificial rules stand in the way of saying what you need to say or letting the song go where it needs to go. Don't write for publishers or anyone else, that path leads to artistic death. Don't think that every line needs to rhyme. Most lines should, but meter and phrasing can make up for lack of a rhyme. Listen to Bob Dylan, and then look at a printout of the lyrics. You'll find that he uses the corniest and most attrocious rhymes imaginable, at times, and at other times he doesn't worry about rhyming at all. Worry about saying what you need to say, and never hold a song back from going some place you hadn't planned on. Don't ever force anything, and if it isn't happening tonight just let it rest for awhile. And finally, write with guitar in hand and sing your lines as you write; your songs will come out more natural and less contrived.

"The earth is not dying, she is being murdered. And we know who is killing her, and we have their names and addresses."
Utah Phillips