I think tempo is the most import thing. You swing as fast as you can whilst able to maintain a good tempo and balance. I allways used to put everything i had into each shot and if i hit it sweet itd go really well, but an average hit was not so good. I then just tried to go for a SOLID contact on my ball, and i tried to achieve this by slowing down and being smoother. I soon found i was hitting it further and straighter by swinging smoothly. After that i had a few lessons and found i was getting much more accurate. So for me tempo is the most important thing. You should only swing as fast as you can while still abale to maintain balance. I hit my driver about 240mtrs on avg and my 7iron 150mtrs with pleanty of hight, and my swing is much slower than alot of pepole i see on the course. Remember to aim for your average shot... not your best shot.