Concentration is a massive part to orienteering that once you have control over, you will be able to have consistence, top performances. I know quiet a few people that do different things to get their head in the right gear before a race to that they are 100% focused and in the right state of mind.
Sometimes people have a puzzle they will solve, or a rubics cube. This takes their mind away from everything else and gets it into a gear of one-two thinking.
I personally need a lot more to calm myself down, so I listen to soft electro music several hours before the race. I also follow my warm-up routine(which never changes) and look at maps before hand. Though I still need to work on getting into the zone...and staying there.
Most of my mistakes happen as soon as I start to be conscious that I'm racing and think to myself "This could be the perfect race" then I mess up. I'm still working hard strengthening my focus for a longer period of time.
Anyways, it's a really big deal to be able to consistenly get your mind into the right place before competitions, especially big ones, so that you can perform to your best ability, no matter how stressed out that you really are.
I would suggest that you start working on a solid warm-up routine that will work for YOU