Problem: Often hitting the ball farther left than intended.

Repairs:

1. You're probably too close to the ball, which cramps your arm into your body and causes you to pull left as you swing.
2. If your swing is at all rotational, hitting early will make you hit too far left. Uncoiling your upper body to generate power is good, but you don't want your racquet swinging around you like a gate. Try to keep the racquet going forward and up.

1. Try extending your follow-through out toward your target more.

Problem: Often hitting the ball farther right than intended.
Repairs:

1. You're probably hitting late. When you pull your racquet back, the tip points at the back fence, and the face points to your right. The face turns forward as you swing, but if you're late, it sometimes won't reach that forward-facing direction.
2. Laying your wrist back on your backswing is an appropriate way to enhance power, but if you don't let it snap forward naturally as you swing, and it's still laid back when you strike the ball, you'll hit farther right than intended.
3. Try extending your follow-through out toward your target more.

Problem: Not enough power.
Repairs:

1. Loosen up! The ball weighs two ounces, the average racquet ten to eleven ounces. If you get a bunch of big muscles all tensed up to hit the ball, you'll be better prepared to push your car out of a snow bank than to generate the racquet-head speed you need to make a powerful shot. Don't try to muscle the ball. You'll hit harder with a loose, quick motion.

1. Use your whole body. Whether you're using the classic forward motion or the more contemporary uncoiling motion, your legs, torso, and body weight should all be contributing to your shot. Don't make your arm do all of the work.
2. You might be trying to use your body, but failing to translate the body's contribution into racquet-head speed. Improper timing is the most likely fault in the classic swing. If you're trying to uncoil, you need to make sure that each body segment's uncoil triggers the next, culminating in the whipping up and forward of the racquet.
3. Your backswing might be too short. The longer your backswing, the more time the racquet has to build up speed.

If you have a forehand problem I didn't address here, direct a message to me (abtennis) in this discussion. I'll answer you promptly.