An uncontrolled Hook (A shot which curves violently from right to left for Right Handers) can be quite demoralising, especially if you know when and where it is going to happen.
Correct analysis of your swing is the key to curing any errors especially with a bad hook. Sometimes the cause can be very minute and difficult to detect, so if the problem persists book a lesson with your local PGA Professional.

Cause 1: Incorrect grip.

Correction: It pays to periodically check your grip. You should have reasonable pressure in the top three fingers of the left hand and be able to see two knuckles on the back of this hand when setting up to the ball. Should the little figures on the left hand lack strength, try squeezing a squash or Racquet ball while watching television. The exercise will help to develop these little used finger muscles which are necessary in swinging a golf club.

Correction: Incorrect alignment is a common cause of the hook. Many people tend to aim too far to the right, which may cause an inside to out swing plane. When setting up to the ball try to get the feeling of aiming a little left of your intended target. The ball should be positioned inside a line off the left heel.