Hi,
I saw this post and thought I would chime in. I'm a big advocate of the Schillinger System, I use his methods for almost all the composition I do. It's a little complicated to break down in a post like this, but I'll mention some basic principals.
He breaks music into several categories: rhythm, melody, harmony, counterpoint, orchestraion, etc. He starts with rhythm and the concepts used in rhythm are later expanded upon in all the other categories, thats why it's important to grasp the concepts in the first chapters.
His ideas are basically ways to take a really simple musical fragment, like 2 or 3 notes and to get endless variations and material out of it by making permutations, geometrically expanding the rhythms and the notes, inverting the intervals (or rhythms), reversing the phrase, etc. It's a pretty awesome concept.
It is all very useful, but I found his chapter on counterpoint particularly useful. I took a counter point class in college and really didn't learn anything about writing counterpoint. Shillinger gives you a couple simple tendencies to follow and that's it. I was able to write good counterpoint right away after observing his methods.
Anyway, I hope this helps someone.
peace, Nicnut