Before every fight, spar or training session I do a whole body joint treatment.
I move each joint slowly and loosely on it's hinge, ball or floating action and prime the synovial fluid.

Andre has a great nack of describing how the above is done best.

If I've got any problematic joint or muscle areas I use Tiger balm to address the problem.

Fish oils are a supplement I take daily, to aid synovial fluid.

In the instance of prolonged injury due to joint injury, Swimming is a great exercise thats not too demanding on any joints.