If you're right handed, shooting left and low/left are the most common issues. You fix this in dry fire (no ammo in the gun, can be practiced a billion times - and then some - at home).
Assuming right handed: keep your right hand relaxed, grip as strongly as you can (literally) with your left hand, and press the trigger straight to the rear without disturbing the sights.
More finger on the trigger? Less? use the pad? the first joint? Magic answer.... *drum roll please*.... it doesn't matter. Do whatever you need to do to press the trigger straight back.
2 important notes for dry fire:
1. ANY disturbance in the sights is an issue. There should be absolutely zero movement.
2. Practice like you shoot. Yes, you can take 12 seconds to perfectly press the trigger back and call it "good." That's not how you shoot. When you shoot in live fire, you do it deliberately and with some form of speed... do that in dry fire as well.