In the everlasting pursuit for distance there is one common thread: swing harder to hit it farther. This is not inherently untrue. If you swing out of your shoes all the time you just might tag one and hit it out of the park. Keyword: might!
A preferred approach to speed and distance is to think about where you are losing speed rather than how you can create more speed. Always remember two things:
1) A loose muscle is a fast muscle
2) Many poor technical positions are preceded by a clench or grab with certain muscles at the wrong time
To illustrate this point I want you to think of a baseball pitcher. His effortless wind up. His left leg up in the air. His back nearly facing the hitter. The ball coming up out of his glove. In time, his momentum builds. His plant leg starts to fall back to the mound and his arm and the ball are heading towards the catcher then--BAM! He unleashes the ball at the precise point he wants to with the complete sequence of motion built up to that one point where he exerts his effort. The ball is off.
In golf, we have a similar sequence of motion as we turn behind the ball, cock the wrists, swing the arms, and start the downswing. Give it time. Let the momentum build then unleash your effort about one foot before impact. This fluid motion will increase clubhead speed and decrease stress on your body. To work on this idea try two things:
1) Keep your grip pressure constant until right before impact. See if you can start with the pressure relatively light then keep it that way through your backswing and especially during the transition.
2) Get set up with the ball on the clubface. From this static set up accelerate forward and "toss" the ball down the target line about ten feet in the air. If you can't get the ball in the air you're not accelerating your chest, arms, hands, shaft, and clubhead at the same time.
We're looking for effortless power not powerless effort. Let the momentum of your swing build until we're finally ready to unleash it at the right moment--impact!