Pick up the sledgehammer with your weaker hand. For instance, the left hand of a right-handed user is the weaker hand. Hang onto it near the bottom end, or handle butt.
Grasp the handle a few inches below the sledgehammer head with your dominant hand.
Choose whether you wish to stand directly in front of your target for a vertical swing or slightly to the side for a diagonal swing. According to RossTraining.com, a vertical swing proves harder to deliver with a very heavy sledgehammer, so a diagonal stance might be your best option if you are a beginner or if you are using a heavy sledgehammer.
Position your feet according to your choice of stance. For a diagonal stance, place the foot on the side of your weaker hand closer to your target, with your dominant foot slightly behind you. For the vertical stance, stand with your feet shoulder width apart, centering yourself in front of the target. You should be only a couple feet away from your target.
Bring the sledgehammer head at the same level as your own head on your dominant side. Lift it into the air, then drive it into the center of your target. Your dominant hand should direct the sledge in its path, while your non-dominant hand delivers the weight of the blow.