Nobody has a perfect swing; in fact, a lot of good players have "flawed" swings. Some mistakes are excusable. However, no matter what level of player you are, there are mistakes you can't afford to make. Here are a few to watch out for.
WEAK GRIP
Traditional instruction says you should be able to see at least two knuckles on the right hand as you look down at your grip, but don't be fooled. The weaker the grip, the more restricted hand action will be, and only two knuckles showing is somewhat restrictive. Unless you are unusually strong and flexible, you need lively hands to keep your clubhead speed up. When you look down at your right hand, you should see at least 2-1/2 knuckles, and three is by no means too many.
HEAD DROP
Maximizing your upper-body turn is tough enough; don't let poor posture make it even tougher. A common mistake is to drop the head at address so the chin nearly touches the neck. This limits the shoulder turn on the backswing. Pay close attention to your address position: Keep your spine straight and chin up, so there's room for your shoulders to turn on the backswing.
FAULTY PUTTER ALIGNMENT
For many players, putting is the key to better scores. Faulty alignment will kill you on scoring putts of three to 10 feet. The common mistake is to line up to the left of the hole, then close the clubface during the forward stroke to redirect the ball back toward the hole. When you feel the pressure of a short putt, that little clubface manipulation becomes increasingly difficult to control. Don't make it harder than it has to be-line up with your body and clubface square to the intended target line.
DRILL: STRING PUTTS
When you practice, take a piece of string with you and run it from the flagstick to a scoring pencil four or five feet away. Then practice putting straight putts under the string. A few minutes a day will improve your alignment.