1. Don't go over the handlebars 1.53 miles into the trail and bounce your face off a rock and cut the whole right side of your body up. This ruins confidence and hurts (me).
2. Don't break your chain 5.7 miles into ride. It is difficult to ride bikes consistently without a chain. Note: carry a quick link with you in case this happens because it can solve the problem (Eric).
3. Make sure your brakes actually work. This improves confidence on downhills, especially if you are newer to mountain biking (Eric).
4. When your friend breaks his chain and has to walk back while you can ride, make sure to stop at every intersection, even if the turn seems completely obvious. When people miss a turn and go the wrong way, this causes unneeded confusion (me).
5. Make sure before departing you don't have dead legs and are well rested, which I thought I was (me).