The only way I've been able to get people to go from shooting basketball groups to tight orange sized groups at pistols ranges is to do 3 simple steps.
1) Assume a correct grip, preferably with the pinky off the pistol and do not cross the thumbs at the back of the grip!
2) Align the sights with the target's center.
3) Squeeze the trigger with the first finger pad excruciatingly slow, with some pistols you can actually feel when the trigger with "break." Squeeze slowly and convince yourself the gun will not go off as you keep squeezing the trigger slowly.