Staying on the bike, and rolling when you can't. I've got a few tar stains from my first few years, but quickly learned to tuck and roll to prevent injury. I don't go over 30 on the trails, or take on jumps over a few feet.
I bought Fox Launch knee/shin guards when I first went from clipless to platforms because I was scared of shin strikes. They're great but the pedals I got (Saint's) grip far too well to be necessary where I usually ride. I'll wear them for shuttle riding but that's about it.
I always wear soft knee and elbow pads when riding, which, right now, are POC and 661 (old straights). But I am not that big in those areas. If you are, then you need to check their fit tables, which are usually pretty close. Also, do not buy so that they easily go on--they need to be a little tight to stay on in a crash and they stretch over time.
Check out the apparel and protection forums also. All sizes of riders there, but you can get an idea of what current protection is working well and how they are sized (run large or run small, etc.).
And they are all a bit hot, but, like wearing a helmet, I am used to it. Feel not properly dressed if I do not have them on.
A forum community dedicated to Mountain Bike owners and enthusiasts. Come join the discussion about bike parts, components, deals, performance, modifications, classifieds, trails, troubleshooting, maintenance, and more!