Go a day or two before and practice on the course, get a run you want to do in the competition down and contiunally practice it over and over. This run should be one you could land no matter what. Then, work on another run, basically a harder version of your first run. If you plan on doing a switch 7 on the last jump, turn it into a switch 9 etc. Your second run should be more difficult than the first- try practicing it a few times to see that its possible, but keep practicing your stock run to make sure that you've got it down.
Come competition time, go with your stock run for your first run (assuming its a two run format). Land this and proceed to step it up on the second run with the second run you practiced the few days before. If you land your second run, you'll be stoked, and if you don't, you still have your stock run score to go on. Normally I have a problem with this and go for my second, harder run for both of my runs, but keep in mind if you do this and fall both times, you're screwed scoring-wise.
Make sure you're well hydrated, had a good nights sleep, have some food in you, and are stretched. Some people like music because it helps relax them, and if this is you, put on a song you've been listening to lately. As well, avoid energy drinks if possible. I personally get antsy enough that the extra energy boost pushes me too far and makes the anxiety even worse.
As you sit in the start gate, invision your run a few times over and make sure you have it completely down in your head. Drop in, and stomp it.
Extra: If you're really feeling good about the competition, crank your bindings down a little tighter before your runs. There is no worse feeling than having a ski pop off for some bullshit reason and having to wash a run because of it. You do take the risk that your ski might not come off when you need it to though.
