1) use a low powered very flexible racquet, great for your arms and control
2) use full natural gut at low tensions, to give you power and great for your arms
3) get the best shoes and insoles on the market
4) play on clay or grass more..
5) play more doubles, hit against the wall, ball machine , light rallying, drills etc.. i.e. have fun.. Playing competitive matches is very hard on the body..
6) massage the major joints and muscles in your body daily like me