Great advice in those first two posts!
I'd add in the following--with an empty pistol, draw from your holster with your eyes closed. Once it's presented, open them. The sights should be lined up with each other (sight alignment), but not necessarily sight picture. If you don't have sight alignment, adjust your grip until you do have it, and do it again. Make this religious.
Second--go on the check out Matt Burkett's grip on his forum. Practice that, and put hash marks on your hands when you have it nailed perfectly--two on the thumb and one on the heel at the centerline of the gun. When you draw, the sights should be aligned and the marks on your hands should be aligned. If not, move them until they are and re-do the exercise.
These two steps are foundational to good repeat shots.
Also--work on your eye speed. When I shoot two shots quickly, I actually see the sights for both shots. It ain't an "according to Hoyle" sight picture, it's a flash sight picture--the front sight somewhere in the notch and surrounded by 'target'. It sounds impossible, but once you have the presentation nailed as outlined above, it just happens naturally.
To improve your eyespeed, try spotting the brass as it ejects and having some idea where it's going to land. Another good one is to fire 3-4 shots as quickly as you can, then mark them on a target by you with a pen where you think they hit. Don't look at the target you just shot until you're done, but then see how close you came with 'calling your shots'. These things will help your pereption speed!
G'luck,
Dan