On the groundstrokes, players with good hands can sometimes get away with bad movement and still make a decent shot. But the overhead is a different story.
Unlike the serve, which is hit from the same position on the court every time, the ball on the overhead is moving toward your side of the court. You can hit an overhead from literally anywhere on your side of the net. The ball is also descending from a much greater height than the serve toss. This is important because as the ball drops, it accelerates due to gravity. For these reasons it is vital to be ready when the ball passes through the hitting zone.
The ability to use Carioka Steps, or what I call cross steps, is the key to moving upward and back. These steps can also be used to move on diagonals across the court when the player needs to move sideways at the same time.
If you want to maximize your ability to move on most overheads, do not rely only on shuffle steps. This is where most players make their first mistake.
Shuffling is an inefficient way of moving either forward or backward. There are many instances where you will see a great player shuffle back or forward to hit an overhead, but usually it is on a ball where they have a lot of time, and/or not much movement either forward or back is required.
They come into play on all the shots in the game at certain times. They are just especially critical on the overhead.
Mastering the ability to rotate your body and then use these crossing steps will increase your speed reaching the ball -- and your power on the overhead. The tough thing about gaining this ability is to be able to do it with the arms moving upwards into the air.
The key to moving backward is to take a cross step backward with the front foot toward the baseline. So the front foot actually crosses over the rear foot in this first move.
In many ways, the best way to practice this crossstep movement is without the ball. Put yourself into the turn position with your arms up and move backward with the front foot crossing in front of the rear foot. Keep practicing it until you can run at full speed and still feel secure in your balance.
Each time you land the rear foot, place slightly more weight on it and relax the knee a bit. That little bit of weight on that leg is important because that is the leg you push off of for the jump overhead.
As you get more confident with this movement you can experiment with jumping from the back leg to make the upward motion more explosive. Most good players do this on most overheads because they are moving back at the time of the hit to deal with the lob attempts of opponents.
Even on a bounce overhead, the crosscourt movement is usually crucial to getting into position quickly. Even when you get what seems like a relatively easy overhead, get into the habit of taking that initial backwards cross step. You will be amazed how fast and far back you can get using the correct footwork.