Fault No. 1
You lean too far left
How you know: You consistently slice the ball
What goes wrong: When you set up with your weight heavily favoring your left side it forces your shoulders and hips open, and you're destined to swing back too steeply and chop down on the ball.
Take your address position with a teed ball, then put the grip of your driver against your chin and let it dangle. The clubhead should point at least 4 inches behind the ball, and that's where your weight should be centered. Keep your upper body steady and return the club to address. Your right shoulder will be lower than your left and it will be easier to set your weight behind the ball as you swing back. This leads to a shallower swing and an end to that chop slice.
Fault No. 2
Your too far from the ball
How you know: You consistently hit the ball on the toe
What goes wrong: Your relationship to the ball causes you to overreach and slouch toward the ball with a rounded back. This gets you up on your toes and makes you lose balance during your downswing.
Stand with your arms extended out in front of you and the club pointing straight up in the air. Now bring your upper arms down so they are touching your chest. Keep that same angle, and bend from your hips to lower the club down to the ball. You should still feel your arms in contact with your chest at address, which will eliminate your reach and correct your posture. From this position you should have no trouble sinking the ball into the center of the clubface.