Let's start with hitting from the top. If you are performing your back swing correctly and you are cocking your wrist, the right thumb will be pointing at your right shoulder. As you start the back swing you need to keep the club shaft as close to your left arm as possible and this is done by keeping that thumb pointed at the shoulder. If the thumb starts deviating from the shoulder it will un-cock your wrist and you will "hit from the top". The remedy for this problem is
to simply relax your hands on the club. Too much tension in your hands translates into your shoulders and upper body in general and will cause you to hit from the top. So just keep those hands nice and loose and focus on the thumb remaining pointing at the right shoulder all the way down.
Some golfers have the problem of distributing their weight during the shot in the opposite way that is required. That is the weight is in the left foot during the back swing and on the right foot during the downswing. This is known as a reverse pivot. One way to correct this is to lift your left foot in the air when you get to the top of the back swing. When you commence the downswing put your left foot down and transfer your weight onto it. It feels very counter-intuitive at times. but with practice this will become second nature.
If your swing is too long it is likely that your right arm is bending more than ninety degrees on the back swing. Try to ensure it does not exceed this angle. Additionally your right elbow should be no more than six inches from your body. If you ensure these two factors are in place when you get to the top of your back swing you will find it difficult to over swing.
Conversely if your swing is too short, you are likely not rotating your shoulder sufficiently. Your left shoulder should be above the right foot at the top of the back swing. As in the over swing, keep the right elbow six inches from your body.
Swaying is another common problem. As with most things in golf it is a two sided problem. You can sway into the ball or you can sway off the ball. As ever finding the middle ground perfection is what we are after. To avoid swaying into the ball your hips should slide until the left knee and hip are over the left foot. Once these three things are aligned, then you can turn the hips to the left. Swaying off the ball happens when your hips don't turn during the back swing but just slide backwards. You must focus on the rotation of your shoulders and hips on the back swing. You can practice by performing the back swing a club length from a wall. If you are sliding, the club will hit the wall. Keep practicing, focusing on the rotation and eventually you will not hit the wall.
Hopefully this article has given you some food for thought about some of the common problems that affect golfers today and some insight into how you can correct them.