Start here, but you have to read the several posts below as well. I wish he had a permalink to the whole set of posts, but he doesn't. He offers this very wise observation:
What non-writers don't know is that it is much easier to write in a formal style than an informal style and much easier to write something long and complicated than to write something short and simple. Writing pop songs might be the best example; like playing bass, it's easy to do badly but very difficult to do well.Yep. Here are the related posts, or you can find the first one in the blog and scroll down.
This is a pop song of utter simplicity, that shows how good pop music can be. I think classical composers have pretty much forgotten how to do this (except for the minimalist guys, but they are pretty maximal these days). But there was a time, when a classical composer was not afraid to do a song this simple: