I have just started being able to control my nerves at competitions. Before I would tremble so bad I couldn't skate correctly.
Try not to watch the people skate who are competing against you. Just as you are waiting to go on the ice, turn your back to the ice and visualize your perfect program in you mind.
Does the coldness of the rink get to you? It always freaked me out! I would take my jacket off to do my program and the cold wind on my bare arms scared me to death! So to fix this, I would jump around before my program. I would do jumping jacks, jogging in place, or just anything to keep my muscles warm.
Talking to your coach also helps, he or she will know what it's like to be nervous.
Take avantage of your warm up. This prepares you for how hard or soft the ice is, and how your blades feel on it. I would get sooo uptight and stiff during my warmup that the ice's feeling would get to me, because I don't compete at my home rink. Just think, everyone is going to compete on the SAME ice as you, so if the ice happens to be a bit harder than usual, you won't be the only one dealing with that problem. Everyone will.
If time allows, watch litttle kids skate. Seeing how they smile and are having fun always makes me forget my nerves and relax.
Hope I helped and best of luck!