Always press straight back on your trigger, do not push it off to the left, or jerk at it.
In rifle shooting the left hand steadies the rifle and prevents this tendency to push off to one side and also in a measure counteracts the effects of snatching or jerking at the trigger.
The pistol has no left hand to steady it. The right hand has not only to aim the pistol, but also to counteract the effect of any jerk, snatch, or push to one side from defective trigger pressing.
It is as well to put in an empty cartridge case and to practise pressing the trigger and trying to have the pistol still aligned on the object the moment the hammer has fallen. Aim and press that trigger at your own eye reflected in a glass and you can see if you pull off your aim.
By doing this you can detect any jerk to the right or left, or up or down.
With an automatic there is a tendency to jerk down so that it is very important not to get into this habit in the preliminary practice with a single-shot pistol.
When you get to grouping your shots well together, you can have your back sight altered so as to put this group into the centre of the object you want to hit, if it does not already go there.
The great thing is to make as close a group of shots as you can; if you group a dozen shots all in a bunch it is good shooting. It does not matter if they are not on the object you want to hit. That is merely a matter of having the back sight raised or lowered to cause the group to go higher or lower accordingly.
Raising the back sight makes the group higher; lowering the back sight makes the group lower.
Putting the back sight over to the right makes the group go to the right; putting the back sight over to the left makes the group go to the left.