- balance of elements (or imbalance to create tension)
- having points of interest in the image, or alternatively lines which lead the eye along some path
- light
Well, the first thing is to think of a good tune...
Or, more seriously:
Why are you taking the picture?
What is your intention?
Who is your intended audience?
Answer those three and all the other stuff follows as a natural consequence.
I always thought of composition as the arrangement of subjects. I never thought lighting was part of composition. I know its very very very important, but I just didn't think it fell under the composition umbrella (thought it was its own thing).