The single best thing you can do for your knees is to pack light. That tent you bought weighs a lot--more than five pounds, trail weight-and you don't need that much space. Trade it in for something that weighs under three pounds and you will save you knees a ton of work. (well, at least two pounds of work!) with every step.

As for walking backwards downhill....please don't. I don't want to find you on the trail and have to help carry you home.

All of this ties together. Pack light, and the rest all follows.