The space you leave open is the space the gun wants to move to. Choke it out: no gaps anywhere on the frame.
Cover the frame
Almost all the gun's weight is in the steel slide; the polymer frame weighs next to nothing. So cover as much of the frame as you can. Get the web of your dominant hand high under the beavertail with no space, wrap three fingers around the frame, and keep your trigger finger high above the trigger guard until you are on target.
Karate chop, roll
With the support hand, lift your thumb to make room, then karate-chop the bottom of the trigger guard and roll your hand forward so it fits like a puzzle piece. No open space on either side of the frame.
Front-to-rear pressure
Do not grip like a baseball bat. Squeeze the frame front-to-back with both hands. The trigger presses front-to-rear, the slide cycles front-to-rear, the recoil runs front-to-rear, so your grip stays in line with all that energy.
Clamp at the bottom
Put most of your squeeze in the bottom two fingers, not the middle. Like stopping a spinning record at the edge instead of the center, clamping low gives more leverage and less muzzle rise. Keep your thumbs slightly up and your wrist locked straight, not canted.
Skip the fancy stuff at first
The support-hand index finger on the front of the trigger guard is for elite competition and tactical shooters. A beginner will use it as a crutch and push the gun off target under recoil. Master all fingers under the trigger guard first.
Weak hands? Front-to-rear grippers, finger extensors, farmer's walks, dead hangs, even a rice bucket all build grip strength. Practice the grip dry at home and hold it hard.