I wouldn't get wrist guards. They just move the energy to your arm and break that instead of your wrists. Another tip is too relax. The more relaxed you are the less injured you will get. I know it sounds dumb, but it's more about being relaxed when you are doing the trick. If you do that then you will be more relaxed when you fall.
This is all if you can though. Things happen and you have natural reactions. These things really only help once you have mastered the park and by that time falling won't be a big concern. These are tips I use when I bomb and catch and edge and fall. I fell going 50mph and rolled it out and didn't feel a thing. Just had to find my hat.
Best advice? Don't fall. That or get pads, but for me they just make you less flexible and heavier.
Im all for having fun, showing your tits and getting fucked up on a river float but it can be done without being a pig.