The only time I hurt myself, I was actually using a table band saw. Just cutting something small (don't even remember what it was.) I picked up a little pice from the side of the blade, and heard a faint (bzzt) and felt a little touch on my middle finger. Pulled back, looked at it, oh whoops. Bled like you know what. Wasn't very deep, but it was pretty long and wide. Got a clean rag and some electrical tape, got it nice and tight, and kept working. Still have a nifty scar about a half inch long.

The only time I've had to get stitches was pretty dumb - it was in 5th grade. Playing "baseball" in the gym with a tennis ball and a plastic bat (it was PE,) and was running, slipped on the plastic base, and slammed into the bleachers. 17 stitches later, i have a scar about 3.5 inches long on my leg, that looks like an arrow, pointing up my leg.

I also broke my arm jumping off the monkey bars trying to grab a chin up bar like a gymnast. I'm not a gymnast... that was in 7th grade

The only car related tip was not something I did but a lesson I learned from someone else -

Don't weld around rags soaked in lacquer thinner.
That, and wire brushes like taking of skin just like they do rust.