I don't really warm up. I know that's bad, but I never have. I would say if you were going to warm up that some light sets of swings as well as some halos would do the trick.
Hang from a pullup bar with your shoulders relaxed and at your ear, arms straight. Without bending the elbows, pull yourself up so that the shoulder move down and away from the ears. That is the feeling you are going for in presses. do a couple reps of that before each set of presses.
"Pavel's Kettlebell Training System—
The Shortcut To Extreme Strength
and Elite Conditioning. Guaranteed. "
Enter The Kettlebell!
Strength Secret of the Soviet Supermen