Writing a lyric is like getting a gig: If you're grateful for any idea that comes along, you're probably not getting the best stuff. But if you have lots of legitimate choices, you won't end up playing six hours in Bangor, Maine, for twenty bucks. Look at it this way: The more often you can say no, the better your gigs get. That's why I suggest that you learn to build a worksheet — a specialized tool for brainstorming that produces bathtubs full of ideas and, at the same time, tailors the ideas specifically for a lyric.
Simply, a worksheet contains two things: a list of key ideas and a list of rhymes for each one. There are three stages to building a worksheet.