well, i'm glad that pjz took care of buisness.

center is boring and doesn't tickle the eye/brain thing (technical term there).
you'll also want to be aware of perspective lines and/or objects outlines, having the lines point your eye towards the goal; not in a "hit you over the head" kind of way...but subtlety. it could just be one object at an angle that leads you.

actually when you look at good artwork and take away the pleasure side to it (damn, those boobs look like they're going to burst!) and technically break it down, i always find it surprising and informative how the artist has used color and framing to add to the total content that we are preceiving.

subtlety is the key here kids.

Comitted to excellence through art.