Here’s my 5 steps to taking better pictures or at the very least a simple iterative checklist that you should go through before each shot. Conveniently listed in order of importance.
Composition – The all important bit (rule of thirds and focal length etc).
Lighting – Patience or perseverance, both may be necessary!
Aperture – Image quality, DOF and falloff.
Speed – Film speed, usually fixed or digital ISO.
Shutter – The final bit in the three piece exposure puzzle.