If I fall forward I put my forearms out and put them parallel to my legs.
If I fall backwards, I do the same for what i do when i fall forward, and just let myself fall.
I just have the add-on of making a fist.
thats a pretty easy way to break an arm. when i fall backwards i just sit down and let my butt hit. when fall forwards i start to sit down and just take it with the side of my body.