Photography is usually instinctive, you see something that catches your eye and you take a picture, voila!
I firmly believe that photography is an expression on one's creativity, you need to understand the rules of composition so you can use them to your advantage and then even go ahead and break them, who doesn't love a rebel?
The rule of odds is a simple principle try to include odd-numbered elements, it will ensure your image is more dynamic, as when you have even-numbered the brain naturally tries to pair and group things.
3 to 5 subjects seem to to be a good starting point applying this principle, its boundless and can be used across all photographic genres.
Give it a try, and let me know what you think.