Khora

Ed's advice is, of course, right on the money!

I would add that you should practice performing in as many different acoustic settings as possible. You never know what kind of acoustics the competition space will have - I did one competition where the room we played in was carpeted, with 8 foot acoustic ceilings, and a cloth covered divider running down the middle of the room Nothing like playing Hummel in a coat closet!

Record yourself, both in performance settings and in the practice room. You will be amazed at how nervous just the mike can make you!
You WILL have nerves. Accept that from the beginning - if you dont' fear having nerves, they have very little effect. You can handle nerves one of two ways - let the nervous energy overwhelm you (be afraid of it+ performance anxiety), or use it to get excited about playing for people.

Obviously you want to avoid any stimulants before hand - coffee, caffeinated sodas (when it doubt, check the label!), sugary food, etc. Also avoid salty foods or anything that gives you dry mouth. Experiment with what works for you well before the competition.

The following is all part of the detailed practice Ed talked about, ways to achieve ownership:
Immerse yourself in the music until you can literally play it in your sleep;

Practice being able to sing through the entire recital, at least in your head, without the horn. Mark in the music any places you dont' feel comfortable singing your part - those are most often the spots that present problems in performance as well. Analyze what you can't sing - is it the rhythm, the interval, the dynamic shift? Fix what isn't working quite right;

Practice fingering through the recital without actually playing, horn not even up to your face. Take note of the places you trip even slightly - raising a valve a little bit too soon, not getting the valves really all the way down, etc. Is there an alternate fingering that makes it easier?

Best of luck - recitals are a lot of fun when you are well-prepared!

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Sandy