How you set up to the ball is going to determine how you hit it. The foundation for a good shot should be laid long before you ever begin to take the club back. The consistency of your golf swing will be determined by getting into the correct golf stance every time you stand over the ball. It will govern your balance and control over your golf swing and furthermore dramatically affect the way you strike the ball.
The first thing to check in determining if you have the correct golf stance is your posture. The perfect position calls for you to bend slightly forward from the waist with your knees flexed. Standing too upright will not allow you to make solid contact with the ball and you will hit on top of it. If you bend over too much you will end up hitting behind the ball so search for the perfect spot in the middle. Your weight should be evenly distributed between your feet which should be spread about shoulder length apart. To achieve good balance your weight should be resting on the balls of your feet and not your toes.
How close you stand to the ball is the next thing to check. Let your arms hang naturally from your side and as you bend from the waist, extend the club until it is placed directly behind the ball. The placement of the ball between your feet will depend on what club you are hitting. For your driver, the ball should be played just inside the instep of your front foot (for lefties this means inside your right foot). As you move to play shorter clubs, move the ball closer to the middle of your stance. For your pitching wedge the ball should be right in the middle of your stance.
To complete the correct golf stance it is critical to make sure that your head is positioned directly behind the ball. The head needs to remain steady throughout the golf swing. Your shoulders should be tilted to make it easier to get the ball into the air. A proper set up means that the front shoulder is slightly higher than the back shoulder at address.