When you pull the trigger, you should do so with the fleshy part of your index finger between the last joint and the tip. If you are not strong enough to pull it there, then move into the last joint—your finger is stronger there. But if you find that to be the case, you should start a program to strengthen the finger so you can position it correctly.
Pull the trigger straight back and steadily back. This helps keep your sights aligned on the target as you pull the trigger.
Move only your trigger finger. Don’t tighten your grip or as you pull or move your arm, for example.
If your trigger has slack in it at the beginning of the trigger pull, take up that slack after your gun is on the target but before you aim the gun for your shot. Then aim the gun. Then squeeze the trigger. You will commonly encounter this on semi-automatics. If you take the slack up after your sights are properly aligned with the target, it tends to pull your shots off.
After the gun has discharged and during recoil, capture the trigger back against the rear of the trigger guard. Then let the trigger back out (reset it) only as far as you have to so that you can discharge the gun again with a single pull of the trigger.