There are a few things that can cause you to hit the ground before the ball, but here are what I see as the most common.

1) The club head is in front of your leading hand before it reaches the ball. I would advise you to try and forget hitting the ball with the club - feel as though you're actually hitting the ball with the back of your hand first. Keep the hand infont of the club right up to the end of the follow through if you can.

2) Ball position. Make sure the ball is not too far back or forward in the stance and not to far away from the toes that you have to really stretch. Many pros hit all their shots off the inside of their left heel. I differ slightly - I use the width of 3 balls. For shots off the tee shots, fairway woods and long irons I hit off the inside of the left heel. For the mid irons I move the ball back in my stance 1 ball with - if 3 balls were on the ground, i.e. progressing towards the target, you would be playing the middle one here. For short irons I move the ball back one more width.

3) Too much body action. This is the most difficult to correct as there are many faults that can occur - bad weight tranference, legs straightening (knees locking) hitting from the top (casting), not keeping body angles. The golf swing is a continous turn and most amatuers, in the eagerness to hit long shots, thrash at the ball, which causes the most mi**** shots. My advice here would be to try and keep the head as still as possible, really force it to stay still in the swing.

Because this last one is a broad category built of many smaller faults I would work on my first two points first. Ideally you should work on them all continually but the point of my reply is to get you moving the ball forward first.

Have fun
Paul