The Right Leg....

1. It can remain with the same flex throughout the entire backswing.

2. It can remain flexed but straighten slightly from the setup position.

3. It can straighten completely.

Unfortunately most golfers straighten their right leg completely on the backswing and this is a terrible mistake to make in the golf swing.

Why?

Because it causes a reverse pivot in the golf swing and as I've already said...that's disastrous. So when you make your backswing you need to always have some flex in your right leg. That's crucial.

OK, I've covered some very important things that need to happen in your backswing. Now I'm going to go over a quick summary of what should be happening, and what and how you should move during  the backswing from the feet up.

        Feet

Your left foot should not move during the backswing at all,  and the majority of your weight should move to the heel of your right foot. Also, you must make sure that the weight does not move to the outside of the right foot during the backswing.

         Knees

During the backswing the right knee should remain flexed. It doesn't need to remain in exactly the same place as it was at address, but it must never completely straighten at any time in the backswing. Now with your left knee you should just let it move naturally where it wants to go during the backswing, you shouldn't try to restrict it.

By the time your club is parallel with the ground your hips should have moved laterally to the right by a couple of inches. Doing this transfers most of your weight to your right foot. But remember, it must never go to the outside of your right foot. Then after that point the lateral shifting should stop and then the matter goes to turning the hips behind you. Doing this causes most of the weight to move to your right heel.

     Spine Angle and Shoulders

The spine angle that is setup at address should be maintained during the backswing. You should not move your spine towards the ball or away from it as you're swinging. And your shoulder rotation should be on a 90 degree angle (or near enough) to the spine angle at the top of the backswing.

Also, you want to turn your shoulders as far as they will go (keeping everything else the same). If you can get your shoulders to turn at least to 90 degrees that's great, and even further would be a bonus. For example, Tiger Woods rotates his shoulders about 120 degrees!

      Head

When you make your backswing your head should move to the right by a couple of inches. So don't try and keep it still because if you do you run the risk of doing a reverse pivot and that's not good. Also, your head shouldn't move up or down at all in your backswing. It should pretty much maintain the same level throughout the entire backswing that it was at setup.

      Arm

In the first part of the backswing the arms should do very little. Then your arms should reach away from the target to create a wide arc. During the backswing your left arm should remain pretty straight. It doesn't need to be kept perfectly straight throughout the backswing, but as you complete your backswing your right arm should naturally bend so that at the top it is very bent. This should just happen naturally though.

     Wrist Cock

At the half way point in your backswing your left arm and club should form about a 100 degree angle. Then at the top of your swing you want your left arm and club to form about a 90 degree angle. It doesn't need to be exact, just pretty close to those numbers.