funny thing is that my favorite drill doesnt involve any actual firing!
I like the pencil/wall drill.
Find a wall, put a sheet of paper on said wall, centered at where eye level is when you're in your firing position. (if you have a landlord or a wife who will get upset about you screwing up the walls of their fine abode, then put a piece of cardboard behind the paper)
put a pencil down the barrel of your pistol so that only about 1/2" or so sticks out of the muzzle. You can also use a pen, but for max training value, make sure it doesn't protrude too far from the muzzle.
Holster your newly made training monstrosity as if you were carrying it (in you carry holster, on your armor, etc. I do this alot with my leg rig)
for about 10 min a few times a week, practice drawing and presenting your pistol by drawing it, pushing it out into firing position (close enough that the pencil should make a mark on the paper without hampering your extension of your arms). Repeat, and try to get your dots on the paper as tight and consistent as possible.
The plus side of this drill is that 1. for cheap bastards like myself it takes exactly $0 of ammo or range fees or gas to work on your draw 2. it never rains on me when I'm doing this 3. it allows me to focus on draw and sight acquisition FORM without the added complication of a target. This works fine in the real world where all i have to do it look at the center of mass, and I bring my pistol up to what I'm looking at.
you can addapt it to trigger squeeze too by leaving the pencil in contact with the paper, and squeezing the trigger.