The Rule of Thirds - Use the space in thirds, like sky=1/3, place the subject near one of the intersections
Groups of Odds - Odd numbers are always more interesting than even numbers of objects.
Rule of Diagonals - Leading Lines in particular can be useful in creating movement and drama in your image. They can also add a sense of depth, or a feeling of infinity.
Space - This rule incorporates two very similar ideas: breathing room and implied movement. If your subject is looking at something make sure there is some "space" for him to look into or move into.
Balance - Patterns and Symmetry
Simplification - empty your background from distraction.
Follow the link to the right and watch the video to see how an actually photographer has applied these rules to his own work.