The underside of the pancake should be a golden brown color before you flip it. You can check this by carefully lifting up an edge of the pancake with your spatula or a fork. The bottom should now feel more solid, and less like batter.
Make sure to use a nonstick pan, non stick cooking spray, butter, or oil so your pancake doesn’t get stuck to the pan. Don’t lift one of the corners of the pancake too much or else you might break the pancake. You may check it often, but use your best judgement. The more you play around with the pancake, the greater chance it’s going to break. You can shake the pan back and forth to see if it slides around. If it does, it indicates that the bottom side has cooked, and it's ready for flipping. If the center of your pancake is too wet and under cooked, there's a chance that hot oil, batter, or butter could splash onto your skin so be careful.