So many people I see setup with their arms bent. If you are doing this you are definitely losing distance on your drives. By full extending your arms you are pre-determining your widest arc. A wider arc translates into more clubhead speed.
First, you need to check your setup to see if you are bending your arms. If so, extend (but not lock) them at setup. This may take a while to get used to but it is vital if you want to hit the ball longer.
Next, do practice swings with this new extended arms position.
Next, hit some easy drives getting used to it. Like any change you may hit some bad shots at first. If you do, you cannot go back to what you are comfortable doing. Keep hitting balls with this new extended position. As you do, tell yourself that you are widening the arc which will give you more power in the future.
So many people quit making changes because they don’t immediately hit great shots. This is one very important piece of the puzzle so you need too incorporate this into your swing if you want more power. So not matter how bad you hit it at first, keep doing it. The payoff will come in longer tee shots.