Mykeal is correct of course.
If I can add my two cents and maybe help out a little I'll mention several things that many people do that can ruin a otherwise good group.
First, understand that a pistol is one of the most difficult things to shoot accurately.
Very small things will move it's point of aim all over the place.
That said, please read on:
People have a natural tendency to subconsciously think that the gun is going to jump out of their hand when it is fired. Because of this, they tend to change their grip by tightening it right when they think the gun is going to fire.
This invariably will change the point of aim right when it needs to be the steadiest.
Another part of this line of thinking is that there is a need to "push back" to resist the recoil of the gun.
The tightening of the grip and the pushing back are very common epically with those folks who have shot Magnum or heavy recoiling pistols early in their lives but it can also apply to new folks who don't know what to expect when the gun fires.
To eliminate both of these tendencies, make a mental note to remember that first, the gun is not going anywhere when it's fired so use a light but firm grip (but not a powerful hard grip) while shooting and just let the recoil "do its thing" without trying to resist it. The gun won't fly out of your hand.
Trigger control is another important lesson to learn.
Some people get the idea that when the gun is on target they need to pull the trigger as fast as possible. They often "jerk" the trigger when they do this and that always moves the gun off of the point of aim.
Squeeze the trigger gently increasing the pressure gradually until the gun fires.
Yes, the muzzle will be moving back and forth slightly from the exact point of aim but it will be a lot closer to the point of aim than it would if the trigger is jerked.
Another error some people make is to not "follow thru" with their shots. They tend to relax their grip a bit allowing the barrel to drop just as it is firing.
Following thru simply means that each time the gun is fired, concentrate on holding the gun "right on target" until at least a second after the gun is fired. Of course the gun will recoil off target when it does fire but in the event of a mis-fire if your following thru correctly, the gun will remain right on target after the hammer falls even if it doesn't fire.
Another thing often done by new shooters is that they concentrate on the center of the target by looking right at it.
It is physically impossible to focus your eye on two different things at two different distances at the same time.
Those who don't believe me on this need to do a little experiment. Hold out your hand at arms length with your thumb pointing up.
Now, align the end of your thumb with something like a door knob or a vase or a similar small object. If you concentrate on the end of your thumb the distant object will be slightly out of focus. If you concentrate on the distant object, your thumb will be out of focus. That's life.
How does this apply to shooting a pistol or rifle?
If you are concentrating on the center of the distant object, who is watching the location of the sights? These sights are the only thing you have to tell you exactly where the gun is aimed so if your not watching them, who knows where they are pointed?
The solution is to focus on the front sight. Although the rear sight will be slightly blurred it will still be clear enough to see that the front sight is aligned with the top of and notch in the sight. The somewhat fuzzy distant target will still be sharp enough to allow you to know where the center is so, keep the front sight on its center and aligned with the rear sight and then gently squeeze the trigger. Referring back to the above, don't even worry about when the gun is going to shoot. Just keep the front sight on target while you gently increase the pressure on the trigger.
If your doing this correctly, you won't know when the gun is going to fire so you won't change your grip and the sights will be aligned with the middle of the target.
Doing these things will greatly reduce the sizes of the groups.
