Good advice from everyone so far..i'll add one thing...
Focus on focus...you don't have to nail the exposure..or the composition, those things can generally be fixed in post processing if you got it close...but you HAVE to nail the focus. Shoot with a narrower aperture than you otherwise might for things that have sufficient light or if you're using flash.
Composition can't be changed in post. You can crop, but composition means choosing your lens length, your height from the ground, and your angle to the subject.

