As you might think, a trail race can be quite different from a road race, both tactically and physically.
Some words of wisdom regarding race day:
First of all, wear those trail shoes. They're light enough for racing, but offer the lateral support you need to keep your feet and ankles more stable. Also, a trail shoe has a heavier tread pattern than a road shoe, and offers a toe "bumper" to protect you from bruising.
Start slowly. In essence, a trail race is a whole bunch of people trying to squeeze onto a skinny trail. Which may make you want to start out fast to beat the crowds. Don't. This will only send you into oxygen debt and sap the energy you'll need later in the race when everyone else is tiring.
Stay loose. As the race progresses, you'll find a rhythm. Imagine yourself as nimble and light-footed as Fred Astaire. In this relaxed state, you'll be less likely to fall and more apt to maintain speed.
Above all, have fun. Trail racing is the most natural form of racing. Indeed, we feel like children as we run through the forest. It's playtime, and we're called to it.
Trail Techniques and Tactics
Whether you are training or racing on trails, think about staying light on your feet. Run as if on eggshells. Also, resist the tendency to favor one leg over the other. A lot of runners start using one leg as the "plant" leg to land heavily on and the other as the "drive" or "push-off" leg. Each leg should do these actions interchangeably.
Some other tactics to remember:
Downhills: Run on the balls of your feet, not on your heels. This means less pounding, more speed and greater control.
Uphills: Shorten your stride, and keep your head up and chest forward. Run relaxed and try to find a rhythm that will take you up and over each hill with relative ease.
Corners: To a greater extent than on the roads, trails offer the chance to round a corner and "hide." Practice bursts of speed when turning corners. Competitors won't see you accelerate, and will experience a mental letdown when they see you've "gapped" them. Include this maneuver as a regular part of your fartlek workout.
Streams: It's possible to cross a stream while barely wetting your feet. All you have to do is high-step across as quickly as possible, allowing your feet to touch down only for a fraction of a second. Try it. And don't be afraid to run right through a stream. Too many competitors lose time by halting at the edge of a stream midrace.race.