With all of your pads on, leave your board back off the ramp and find a spot that no one is riding on. Now, run up the side of the ramp, jump, and land on your knee pads. You should slide down the ramp to the middle, and it should actually be kind of fun. Do this a few times, and get used to it. When you are riding the vert ramp and fall, this is how you want to do it.
Sometimes, though, you won’t be able to. You will fall on your side, back, head – whatever. The first thing to do is to not catch yourself with your hands, unless you are wearing wrist guards. But, just like I said back in Just Starting Out Skateboarding, I highly recommend not getting into the habit of catching yourself with your hands. Try to roll onto your knees. But whatever happens, the main thing is to just relax and let gravity pull you down to the middle of the ramp.