Eliminate vertical head movement. Also try not to come in too steep in the down swing.

For thin, or topped shots, are you flipping your wrists before impact? I try to picture my left arm and shaft in line with each other at impact. This ensures flush and square contact. Fat shots are usually from coming in steep and squatting in the down swing.

Reverse pivot (not loading weight on rear leg) will also limit your success in returning to the same spot your swing started at address.  If you have a I-Phone or an I-Pad or have a good friend that does, the (free) Titleist App will allow you to capture your swing and you can compare that to the pros available through the app.  Notice when you start your swing (arms or hips first?) and compare swings all the way through.

The guys on the School of Golf, as well as other online sources will also look your swing if you think your swing looks just like Jason Duffner or Bill Hass's swings.  Local retailers or pro shops may also offer reasonably priced lessons with video to view.

There is a message chain somewhere on here on What was your favorite tip?  Lots of good stuff there, too.