Most people who have ridden a bicycle have crashed or had an accident of some sort.
Forgetting the obvious, "Don't get hit by a car", what other ways have you crashed or had an accident?
Was it due to rider error or was it unavoidable?
I'd like to gain wisdom the easy way, but hearing about your mistakes so that I can avoid them.

Or on the other hand, if you have a perfect record, what kinds of precautions do you take to keep that frame scratch and broken bone free?

I'll start with my most recent fall, which was last year. I was having a great ride, zipping through a parking lot. After successfully avoiding three cars who were not really aware of me, I was definitely aware of them, I got cocky. Zipping around a telephone pole and back onto the sidewalk, I took the turn too quickly, tried to compensate, but ended up losing traction on the back wheel and went down.
(I don't usually ride on the sidewalk. Just that short stretch since it's very bike unfriendly.)

Landing on my side, I ended up bruised and embarrassed, but not seriously hurt. I take that turn each day with a little more care.

How about you?