My advice is to learn skills first then start trying tricks... In mountain biking most accidents occur because the rider is either trying something over his head and/or he doesn't have the skill to deal with the terrain. It's always best to ride with caution until certain skills are mastered. If you think in the beginning you can ride like a professional, then yes, you will get hurt. Many people start out that way... too impatient to take it easy and learn how to tackle terrain first.

Here's what I do to address skills... if I have difficulty with something, say steep, narrow switchbacks (my nemesis), then I ride them over and over and over again. I ride them until it becomes second nature. Obviously you want to jump things 1) is your bike set up for it and 2) do you know the basics? Think about taking a skills class...

I won't address riding without a helmet, you already know how dumb that was... not certain well you feel the need to wear pads unless you are freeriding but if it makes you feel better OK. Another thing, do you know what to do in a fall (ie do you know how to fall properly? Arms in, head tuck, roll...)

Anyway remember you aren't 6 or 7 anyway and wont heal as fast plus if you are like me, you have to work on Monday so be careful...