Helpful list from Scott Bourne, a leading photography blogger and educator, with the delightful reminder… when in doubt, leave it out. (Note, post edited in response to Mr. Bourne’s concern that I had quoted too much. No offense intended, I’m happy to use a non-infringing excerpt. It was truly the last item in the list that attracted my attention.)
1. Use negative space. 2. Avoid merges. . . . 15. When it doubt leave it out.
For the full list and much more, see the author’s website: Composition – Basic Tools – 15 Quick Tips « Photofocus.