Don't be afraid to write bad songs and then start over and re-evaluate. Songs are like plants, in that you grow them. Some grow really fast, and others need pruning and care...And, finally, a song needs to move you. If it doesn't move you, it will never move anybody else.
There are happy blues, sad blues, lonesome blues, red-hot blues, mad blues, and loving blues. Blues is a testimony to the fullness of life.