Point gun in a safe direction and keep your finger away from the trigger guard. Then hold the slide as tightly as you can behind the ejection port with your palm on one side of the slide and your fingers on the other side using your support hand.
Then take your dominant hand and slam it forward on the rear of the grip making sure you grasp the gun with the dominant hand at the moment of impact so as not to drop the gun. This technique has worked for me. . Be sure to keep the gun pointed in a safe direction, keep your finger away from the trigger and don't drop the gun.