The most basic and important thing to learn is the roll. To further yourself from harm while doing parkour it requires a strong hold on yourself and training. Before you can jump off roofs,  small inclines and do crazy stunts you MUST learn the roll. It may take many tries but you must practice. Sadly if you do not work hard enough to perfect it, it can kill you. Imagine falling a three stories and not doing a roll, all that your left with is your body broken, crushed and possibly in pieces. There are some other issues that come along with that risk. Families, Friends and people in your life may care about your well being, if there is a stunt that you think you can’t handle then please don’t try because you need to do it. Be smart take it step by step and Learn your rolls.