Composition

Use of light--back light

Cool Light and Simplicity of Design

Symmetry

Simplicity

Repetition of design

Rule of Thirds

Point of View

Composition is a big part of image making even before you start manipulating them in Photoshop.  In fact, I believe that you should try to get the best possible photograph in-camera.  Above are some "rules" for arriving at a good photo visually.  I think that most of them are self-explanatory.  And, more important, is to arrive at what a photography professor once described as "punctum."  I think he meant something that grabs the eye and the heart of the viewer.