How NOT to injure yourself

I don't believe it. I've been climbing away, really watching myself to keep myself fit and unhurt from any silly injuries that could ruin my long term plans with climbing/running.
And then I slipped off the wall on Monday night. On the arete. And hit, make that cracked, my knee of the hold on the way down. owwwwwwwww.............
Well, my knee now crunches and the physio has said no running for a few days. Oh well, it could be worse - looks like I've just bruised the bone so badly my body can't decide what is injured so all my muscles keep contracting in shock! Never heard that one before, but hey, don't physios know everything :)