What are you trying to accomplish with your grip? First of all, you want to make sure the gun stays in your hands when you shoot it. Even more specifically, you want the gun to stay in a good shooting position in your hand when you fire it. But how can you accomplish this when there is recoil occurring?
Remember that energy always moves to the place of least resistance. This means that the energy from the recoil will tend to move to whatever area has the least amount of control on the gun. If your support hand has a weak grip, the gun will tend to recoil up and sideways toward your support hand, causing you to have to re-adjust your grip after each shot. A good grip allows the gun to direct all of the recoil energy straight up, minimizing the need to re-adjust.
To accomplish this, start with your strong hand (the one containing the finger you intend to use to activate the trigger). Take the webbing between your thumb and trigger finger and push it as high up in the backstrap as possible. This is the area found on the very top of the grip (sometimes mistakenly called the handle) of the pistol. Leaving the strong hand low on the grip is the first mistake usually made by those that have not been properly trained.
Now that you have your strong hand firmly in place, make sure that your finger is OFF THE TRIGGER. It should be indexed, or resting along the side of the frame of the firearm, NOT resting on the trigger guard. From here, you will want to wrap your remaining three fingers around the grip, directly under the trigger guard. Finally, take your thumb and raise it so that it is nearly straight up on the slide.
Remember, if we are going to take the time to shoot with two hands, then we need to grip with a purpose. Take your support hand and rest your extended thumb on the support side of the pistol frame. Start about halfway forward on the slide (but don't let your fingers wander in front of the muzzle). Gently slide your support thumb back until you feel the bone (at the base of your hand) catch underneath your strong thumb. If you have done this correctly, your support hand should be angled slightly downward. Rest your strong thumb straight down on your support thumb.
From here, you will want to wrap ALL FOUR support fingers underneath the trigger guard, and around your strong fingers. For some reason, many people like to take their index finger and wrap it in front of the trigger guard. This will cause definite problems with your accuracy. All four fingers should be underneath that trigger guard.
Try taking your pistol (ensure that you have correctly gone through the unloading procedure first) and holding it in your strong hand only. Aim at a target. Now simply squeeze with an even tighter grip. Did you notice that the muzzle began to point up and slightly away from your strong hand? If you have noticed your shots typically landing in this direction, you have probably just figured out why, you are gripping too tight with your strong hand....typically right at the time you are ready for the bullet to discharge. This is caused by anticipating the shot. As we discussed in stance, the brain HATES recoil and it does everything it can to trick you into helping it avoid it.
To account for this, you will need to adjust your thumb position. To do so, you simply need to move your support thumb out from under your strong thumb. Bend your strong thumb slightly down. Now place your support thumb over the top of your strong thumb with a little pressure.
By following these tips, you will now have solid control of your firearm. So go on... get a grip!