Firstly, to understand how to become a power hitter, we need to analyse why the average golfer loses power, and hence distance.

Teeing up the golf ball too low
With the ball teed up too low, the driver is not able to sweep the ball away, but tends to force a steeper downward hit. The thought process came from an earlier period in golf, when the sweet spot was low down on the driver head.

The latest drivers have a larger sweet spot, and the sweet spot is higher up the face to give more spring effect.

To overcome this problem, tee the golf ball up, with at least half the ball above the top of the driver head.

Stance too narrow
Most average golfers have too narrow a stance when setting up to the ball. This tends to lead to an unstable base, and hence poor balance.

To overcome poor balance, a slightly wider stance is used with your toes slightly splayed out. The lead foot should be splayed out around 30 degrees.

At address the hands tend to be too close to the body.
This tends to give the club a narrow arc.

Really good players when using the driver will reach a little more, producing a much wider arc, dramatically improving their distance.

Swaying during the backswing.
There is a tendency to sway backwards, instead of turning about a pivot point. The weight is too much on the outside of the rear leg.

By all means move your weight to the rear leg, but only onto the inside of the trailing leg. Try turning more than swaying backwards.

Keeping club close to the body on take away.
This definitely loses you power.

Extended your arms away from your body, as if handing the club to someone to your right, whilst still maintaining your balance.

Keeping right elbow too close to your body at the top of your backswing.
A lot of average golfers will keep their right elbow too close to their body at the top of the backswing. There will be a loss of power here.

Ensure your right elbow stays out from your body, which in turn will induce a much wider arc, and hence more power.

Reverse pivot.
Reverse pivot is a big loser of power. This is where the weight tends to go towards the front leg on the backswing.

Overcoming this weight shift means concentrating on moving your weight onto your back leg, but not too far.

Ball position wrong. There is a tendency to put the ball too far back in their stance.

The golf ball should be roughly opposite the left heel to allow for a nice sweep of the ball by the driver.

Left foot leaves the ground on the backswing.
By allowing the left foot (or trailing foot) to leave the ground on the backswing, this will not allow the body to wind up like a spring.

Keep the left foot down and turn your shoulders against the resistance of the lower body. This is a great way to get a nice coil for power.

Swaying on the downswing.
Average golfer will sway forward during the downswing.

To keep the power, move the hip slightly in a lateral movement, and start the club down, with the right arm tighter into the body.

Flipping the hands.
Some golfers have a bad practice of flipping the hands.

By keeping the hands cocked this gives a nice lag, and plenty of stored energy.

Hands too high at finish.
Having your hands too high at the finish produces a weak finish.

Allow the body to come through naturally, hips rotated over the left leg, allowing the right heel to come off the ground.

These tips will definitely get more power into your golf game. However, if you are still struggling and would like some good drills to help you, then a good place to visit is:- http://www.thegolfprofessor.com/practicedrills.html