Most tennis myths arise either from a misstatement or from an overgeneralization of a correct principle.
Myth #1: "You should make sure to snap your wrist on your serve."
This is the most popular and most harmful of all tennis myths. If you snap your wrist deliberately on your serve, the only thing you're likely to accomplish is eventually injuring your arm. Keeping your wrist loose on your serve will let it whip forward exactly when it's supposed to -- as a natural consequence of the forces generated by larger, more powerful parts of your arm and body. Trying to snap your wrist deliberately can put its motion out of sync with those powerful forces, and this can lead to injury. You don't need to think about snapping your wrist, and you definitely should not try to force it to happen.
Myth #2: "You should always plant your feet to hit a volley."
When you'll be making contact below the top of the net, volleying will be easier if your feet are not moving, but on higher, slower balls, unless you're already quite close to the net, you'll do better by continuing to move forward as you strike the ball. This will get you closer to the net for your point of contact, and more importantly, it will help keep you from stopping in the midst of hitting the ball. When you stop moving, your body tips forward, and if you're trying to hit a ball while this is happening, you'll tend to pull the ball downward into the net.
Myth #3: "You should stop to hit an approach shot."
If you have time to stop and set up before you start your swing on an approach shot, you'll be able to execute a bigger swing more cleanly than if you are still moving, but, if you try to stop in the midst of hitting the ball, you'll be off balance, and you're much more likely to commit an error. If you don't have time to stop well before you hit, then keep moving forward as you hit. As you near the ball, you'll usually have time to slow down a little, and this will make it easier to execute your swing.
Myth #4: "Roll your strings over the ball to produce topspin."
Amazingly enough, one still hears this little gem of goofy advice being given to unsuspecting tennis students. The last thing you want to do is try to rotate your wrist while you're hitting a forehand or backhand, and it's simply not possible to roll your strings over the ball: the ball is on your strings for less than 1/100 second. Trying to roll over the ball will only make you turn your racquet face too much upward or downward, causing an error.
Watching the pros on television
as they play at Roland Garros can be deceiving. While it appears that they regularly
hit shots that skim just inches over the net, that’s not the case. Although
the camera angles used for TV don’t show it well, the pros hit most of
their shots several feet—and often several yards—over the net. This
is a smart thing to do for several reasons. Good net clearance gives you:
Safety: Many recreational players think that hitting low over the net is an advanced way to strike the ball. While there are many times when hitting low makes sense (such as on passing shots), the pros know better than to build their games around low-percentage shots that just clear the top of the net. One easy way to add more margin for error to your game is to hit higher.
Depth: For the most part, the higher the ball goes over the net the deeper it will land in the court. Depth is one of the most important qualities of a well-played shot. Although you can hit deeper by hitting harder, it’s easier and less physically taxing to do it by aiming higher over the net.
Variety: Even though you may not have mastered spins or changes of pace, you can still add variety by occasionally hitting higher over the net than you normally might. You’ll likely discover that many of your opponents are bothered by high-bouncing balls, especially if they’re deep in the court and directed to their weaker side.
Myth #5: "Stay down with the ball."
This is more of a misstatement than an outright myth. Pulling up too early on a forehand or backhand is a mistake, so staying down until the right time is good, but you don't want to stay down completely through the entire swing. Except on certain slice shots, including drop shots, you generally want your legs to push upward as you swing. On most swings, you don't want to stay down -- you want to be on your way up.