Participate in a regular exercise program. The ideal form of exercise for musicians would provide good aerobic training, involve the upper body, and be unlikely to result in injury. Swimming is an excellent all-around exercise. Aerobic dancing classes, rowing, and cross country skiing can also be beneficial and low-risk. Nautilus equipment can provide good conditioning, but be sure to get proper instruction in its use.
Exercise is a good tension and stress reliever, too.
Obviously, you should work closely with your teacher to develop and maintain good technique. You may wish to talk to your teacher about taking lessons in the Alexander or Feldenkreis techniques. Aches and pains must not be ignored. Pain related to overuse can start during the practice session or several hours later. Overuse problems may be especially likely to start during periods of increased stress.