hi, imho, the first 18 inches straight back and i mean straight back..(when your hands are in front of your right knee, the clubhead is just right of your right foot and still on the target line,).. is the most critical in the entire golf swing. Do this by pulling back with the two middle fingers of the right hand. Keeping your right knee in the same position as address to the top, you cannot come close to turning your left shoulder 90 degrees. unless you have trained like a pro, but you don't need to. What you need is normal wrist cock and retaining it thru impact. Your right elbow cannot fly if your pivot thus is correct cause you cannot turn shoulders far enough to let that happen and you can hit as hard as you want with your right side, for a right handed golfer that is. You will find it easier to make solid contact and as you get use to it you will hit it further than before when timing gets better. Give it a try and tell me about it, it has worked for me after 40 years of frustrating golf.