There are all kinds of "rules" in photography.  Remember it is okay to break them.  However, if you are practicing one of the "rules" or something you want to accomplish take time to look at your photos on your camera screen.  For example, if it is the rule of thirds, do you think you nailed it in-camera?  Try putting the subject in various positions on the "grid."  Even consider centering it just to see if it works.