I'm going to respectfully disagree with Bert about the 3-minute rule. I'm not sure it really applies to commercial songwriting anymore; besides, a lot of really great songs are longer than three minutes. Some time ago I heard a radio interview with Ray Price, who said you can tell when people write for a market, because the songs have no heart. You can hear when someone's just writing for the paycheck. I also heard Tom T. Hall say that people should write what they feel - I agree wholeheartedly. A good many of his songs break traditional songwriting rules, and no one can argue that he has had a splendid career.
A long time ago I was at a club watching a songwriter I really admired. I said to my friend, man, I wish I could write like him. And my friend said, don't write like anybody but yourself.
Sometimes they fall out of the sky. Sometimes they don't. But I've found that too much forcing is evident in the final product, so I don't force anymore. I just coax gently. :) But everybody has their own way. -------Kim