Wear comfortable shoes and be sure not to overplay. I developed a chronic knee injury from playing too much and too often on hard courts. Oh, and whatever you do, don't try to slide on cement. I assume that you've mostly played on clay (since you seem to be from Germany), so I have to warn you that though sliding may seem natural, you wouldn't want to try it on asphalt.
Best left-right combination by a German (and that includes Max Schmeling): Steffi Graf. All she did in 1987 was knock Navratilova out of #1 and try to knock Evert out of the sport. (Mike Lupica in "The Best and Worst of Tennis in 1987", World Tennis)
"A couple of years ago, we nicknamed Steffi Graf's forehand 'Jaws'. And that music would go perfectly when she starts running in to the net, swarming on that little ball." (JoAnne Russell, during the 1988 Wimbledon final between Graf and Navratilova)