Not over-doing it when you're tired is one of the many things I've learned from auto racing that transfers directly to bicycles as well.

I've been racing cars for over a decade (instructing at auto-x and HPDE's for four) and one of the most important things I can tell students is not to push it during that last session on Sunday. If anything they should back off. They all want to go that little bit harder on the last session - to prove what, I don't know. But after hours in the car and standing around a hot asphalt slab, pushing harder during that last session when you're physically and mentally drained can turn a fun weekend at the track into a really, REALLY bad weekend.

Side note: It may suck to taco a wheel or crack/dent a frame, but it's nothing ($$$ wise) compared to putting a car into a wall or on its roof.

The other (biggest) thing I've taken from racing is vision. LOOK AHEAD. Number one rule. When I'm riding, say 3rd or 4th wheel in a group ride, I consistently notice and point out road hazards before the riders in front of me. I HATE the hazard signal that comes from the guy in front of you as his rear tire is passing the hazard - you know, the "Oh BTW, don't run over that thing you just ran over" notification. Seriously, get your eyes up above your front wheel.

Mac