Proper form. There is a lot more to lifting weights than people realize. It all starts with learning and studying how each movement is correctly performed Im 53 years old and can still out lift most guys younger than me because I learned how to lift weights early on. My joints still feal great. Also listen to your body if something doesn't feel right stop dont do what many have done and think a minor twinge in a specific joint will magically just go away it will only get worse.