Look where you want to go, not where you're at. Don't focus on your front wheel.
Along those same lines, don't look at something that you want to avoid. Want to miss that tree that's right at the edge of the trail. Don't look at it; look past it. Target fixation can get you hurt.
Make sure your bike is ready to ride before you start your ride. Tires are at pressure, sag is set, chain is lubed, shifting is good, brakes are firm. You'll have a better time and so will your riding buddies.
Never forget your helmet and eye protection. Forget your shin guards; take it easy on the ride. Forget your helmet; find one or don't ride. Nothing will ruin your day faster than a rock to the head or the end of a tree limb in the eye.
It's OK to say hi, even wave. We're not road bikers!
And I'm spent...