Left Handed Golf

Its really not enough info to answer why YOU hook your shots but here are a few common reasons why hooks occur:

A hook (for right handed golfers) occurs when the ball starts to the right of the target line and then curves to the left to finish to the left of the target.

Clubface closed?

Check the following list for possible faults:
Aim: Your clubface may be too closed.

Grip: One or both of your hands may be twisted too far to the right. Check the V formed by your thumb and forefinger – it should be pointing inside your right shoulder, not outside.

Ball position: The ball may be too far back in the stance.

Stance: Not usually a problem but may be too wide.

Ball too far back in stance

Body alignment: Shoulders aimed far too far to the right. (See above).

Posture: Not normally a factor.

Swing: You cannot hook the ball unless your clubface is going crazy through the strike. Generally the swing is too long so, the body gets to the ball before the club head and the hands turn over at the last minute. (See above).

Golf coach tip: Keep the swing nice and short.

Here’s my favorite tip: lessen the grip of your top hand.
The weaker the top handed grip, the less likely you club will flip over.

A hook comes from two main causes.

1) An inside to out swing path. This imparts a hook spin onto the ball. The ball starts right and hooks (or draws) back to the left. To cure this, make a box out of six tees by making two parallel rows of three tees each. The rows should be about 12 inches long and 6 inches apart.
Looks like this:
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swing-path
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Practice swinging with your driver making, the club path go through the box (i.e. through the two parallel rows) without hitting a tee. This exercise will help you see flaws and teach you to swing straight through the ball.

2) Hitting the ball with a closed club face. This usually makes a snap hook that starts left and keeps going left… (as you yell: “Noooooo!”)
To cure this, adjust your grip. The vee (shape between your thumb and index finger) on your left hand should point toward a spot between your chin and your right shoulder. The vee on your right hand should point toward your right shoulder. You can adjust by turning your right hand to left (counterclockwise) to make a more open face at impact and to the right for a more closed face.

Hope this helps.

PS
One of my favorite lines: “The best way to hook the ball is to try to slice it”.