I love looking at data to help me understand patterns in sports. So when I asked myself what is the best height to hit the ball over the net with, I figured I should look at the pros to figure this out. As you can see below, the stats of the pros show that you can have a variety of heights and still be successful. So the question isn't about the height, it's more about differentiating your forehand vs backhand as well as your type of playing style. Let's take a look.
Forehand vs. Backhand
Most players had a different net clearance for backhands vs forehands. This is important for your to consider. To figure out what is best, spin has to be considered. Do you hit with a lot of spin or not as much? The more spin, the higher over the net you can aim. Also, if you have a weaker backhand vs a forehand, it is best to not lose on your backhand so playing conservatively (high over the net and deep) is your best bet.
For the most part, the stronger servers have big forehands. Bigger forehands also means hitting flatter which then means lower over the net (otherwise the balls will go long without the added spin to keep the ball in). This is the case for players like Del Potro, Isner and Federer. While players that do not rely on their serves as much have a higher net clearance on their shots such as Nadal, Gasquet and Robredo. Figure out what your style is and adjust your net clearance to that style. The more of a counter puncher you are, the higher over the net you should aim. The more of an aggressive player you are, the lower over the net you should be aiming (within reason).
Although the amount of clearance you hit over the net can vary, it's only by a foot or so with the pros. two feet seems to be the happy medium so consider giving yourself at least that much amount of height to allow for room to miss and still get the ball over the net. The more you work on targets and focused practice, the easier you can do this in your matches without thinking about it.
Want to learn about the one handed backhand? Here's some tips from Javier who I stayed with in Spain that teaches tennis in Madrid.