Does your pistol target look like the one above? There is a very high probability that the problem causing low and left shots has nothing to do with the sights on your pistol. It is most likely a small mistake you are making with technique.
Quick Answer: Low and left shots are usually caused by having too little trigger finger (closer to the finger tip) on the trigger, jerking the trigger, and / or flinching before and during the shot.
What are the most common fallacies?
Stance could affect the grouping and off centering of pistol shots. To some extent this is true, but unless you are standing on your head or in some very awkward position, stance is not the cause of shooting low / left. All you want to accomplish with stance is to give yourself a platform to shoot from that is stable by allowing the pistol to naturally point at the target. From that point, just try to have shoulders over feet which means there should be a slight forward lean if possible. This is all you can do with stance.
Grip is also another variable that some will say affects your accuracy. Again, there is some truth to it. If you are not using the standard pistol grip and are doing something strange that points the pistol away from the get, improving grip will help.
The two handed grip for semi autos above is the standard grip. You should do you best to duplicate this. The pressure you apply should be about the same as you apply to a hammer when nailing. Strong and tight, but not so much as to cause your hands to tremble. The pistol should be comfortable in your hands.
If you have accomplished this and someone tries to change your grip to stop you from hitting low and left......don't listen. I will explain my reasoning for this now.
All pistol grips and length of pull dimensions (distance from trigger to the heel of your hand) are different for every pistol. Our hands are also different sizes and shapes. Putting these two facts together results in many variables that can exist from one pistol / shooter combination to the next. To expect one pistol technique to work for everyone on all pistols is not realistic.
Just duplicate the grip above to allow you to maintain a very firm grip on the pistol. Finding exactly the right position for your hands and pistol will also help tremendously in managing recoil.
Sights are off. This could cause you to shoot low and left but 99% of the time it is not the true cause. Especially when some shots are close to the bull and others spray low and left. Don't get into the circle of adjusting sights until you are sure your technique is not the issue. I have seen people go through boxes of cartridges while trying to tune their pistol sights and never seem to get them just right. That is because their technique is the true source of the problem.
If you are the person who has one of those 1% pistols, when the sights are truly off 1% of the time, you should be seeing a tighter group, tighter than in the picture at the top of the page, in one spot. In that case, move your sights slowly and only in small increments. You should immediately see the group change positions.
What are the true causes of shooting low and left?
Position of trigger finger. The largest cause of shooting low and left is incorrect position of the trigger which prevents the trigger being pulled straight back along the center axis of the pistol. In other words, because of the position of your finger on the trigger, you are torquing the pistol left and slightly low during the trigger press.
You need to find the correct spot on your trigger finger. If you are shooting to the left, put more finger on the trigger, or the trigger closer to the first joint. If you are shooting to the right put less finger on the trigger or closer to the tip of your trigger finger.
When dry fire practicing, you will know when you have the right spot when you can squeeze off a shot, and the front sights don't move - at all. It doesn't take much movement of the trigger position on your finger to make a big difference in where the shot impacts, even at close range.
Jerking or slapping the trigger can be another source of shooting low and left. This action versus a smooth and steady press of the trigger can cause shots to be low and left.
To be honest, if you are pulling the trigger straight back along the centerline of the pistol, as described above, jerking or slapping the trigger really doesn't matter, as long as you can do it without the front moving at all.
Make a smooth trigger pull instead of a jerk or slap. This just requires putting your focus on it. Use the trigger reset to minimize the distance your finger travels when executing multiple shots. This will help tremendously. For more information on how to shoot more accurately and faster, check out this article.
Flinch is another main culprit of the low and left shooting pattern. This usually occurs when the shooter is recoil sensitive. Once you have the flinch it is hard to cure. In anticipation of the noise and recoil, your brain is telling your arms and hands to move.
Experienced shooters can sometimes make their minds ignore the recoil and blast consciously. After a few shots they are right back on target. Most of us can't do that successfully.
Moving back to a smaller caliber like my 22 M&P works most of the time for me. After a few rounds I can normally eliminate my flinch and get back on target.
Shooting low and left with a pistol is something that most newer pistol shooters fight until all of the processes above become second nature. Make every trip to the range count by making sure you fix one of the true sources mentioned above. In no time, you'll be shooting tiny groups and people around you will be asking you for tips.