Listen to music you don't usually listen to and pick out some phrases you like the sound of. Chuck them down on a piece of paper in no particular order and try and think of some different words describing those phrases (by this point, it definately helps to know the topic of your song). You'll find you'll probably come up with some words that you reckon would sound real cool in a song. Use your words to link some of the ideas taken from the other songs, but make sure you're not directly taking anyones stuff, not only is it plagiarism, but it's degrading as a musician to break the unwritten law.