Many people complain about not being able to hit the ball well with their woods (or metals) and in particular their driver, even though they can hit an iron shot as sweet as you want. The major reason for this is generally poor quality of contact for many of these players.
Here is a simple exerercise to help. Put a tee in the ground (without a ball) sticking up about 2.5 to 3.5 cms. You should be able to strike the tee consistantly WITHOUT hitting or even brushing the ground at all. If you miss the tee, or touch the ground or even worse gouge a trench out of the ground don't wonder why you cant hit that ball 300 m plus !!! If you strike the tee, then needless to say you are going to have a solid contact with the ball, which is the first pre requisit to a good shot. The longer the shaft on the club then the more practice it is going to take to master this technique and the more presision required. Remember your distance stance will be slightly different for the driver to say a 5 metal due to the varing length of the shaft.
Once you can consistantly clip the tee without touching the ground or even the grass then you can move on to direction control and the 101 other things to get right !!