The best way to protect your joints when using them is to use your head first. If you're constantly bending over to work in your garden, can you create a raised flower bed instead? Instead of picking up an object from one end of a table to put it down on the other end, can you slide it instead?
Another "joint-smart" approach is to back off when your joints start reacting badly to a certain activity. It's smarter to put the activity on hold and rest your body (or check your e-mail) before returning than it is to power through the activity at the expense of your body.
Plan your day and arrange your activities so they're not all grouped together. If you have several projects, schedule a more intensive one between two simpler tasks to allow your joints plenty of rest. Don't overestimate how much your joints can handle. If you're pulling, grasping or carrying an object, change positions frequently if you feel stiffness coming on. Affix easy-grip pads to handles and knobs to help you turn or grasp them.
Decide if the task at hand is worth the toll it may take on your joints. Can you hire someone or call in a favor to get the task done? If you can sit comfortably instead of standing during a task, do it.
Your joints will thank you for thinking of (and for) them.