Even if you have your sights aligned perfectly, the manner in which you pull the trigger could cause your shot to go off target. You should make sure that when you pull the trigger all the force on the trigger is being applied in a straight line in the direction that the trigger moves (towards the rear of the gun). There should be no force to the left or the right, or upwards or downwards.
THe way to do this is by placing your finger on the trigger about one third of the way past the first knuckle, towards the tip. This will ensure that when you pull the trigger you’re not pushing or pulling the muzzle of the gun away from the target.
On a personal note, for me focusing on this caused the greatest increase the accuracy of my shooting.
You can practice this by doing dry fire practice. Make sure your gun is safe (no cartridges in the magazine, and none in the chamber). Move to a room where there is no ammunition, so that there’s absolutely no chance of mistakenly firing a cartridge. Point your gun in a safe direction and pull the trigger. You will have to pull back and let go of the slide before every trigger pull because you won’t have the recoil of the previously fired cartridge doing it for you.
When you dry fire like this you can focus on the mechanics of pulling the trigger and can also see if you’re anticipating the recoil.
Speaking of which: Continue reading: Shot Anticipation