Hi:
When anyone appears in front of people, whether playing a theremin, performing a play, or even giving a quarterly company sales report, it's normal to be nervous.
Others above have provided you with sound advice.
There is another aspect to the issue of nerves and playing well that has more to do with your approach to the instrument every time you practice. Of course, playing the right notes, practicing your technique, training your ear -- all of these pretty much go without saying. But none of them deal with a very real barrier that goes to the heart of the desire for perfection. This desire, along with nervousness, are two emotional states that feed off one another.
The very notion of playing flawlessly is self-defeating. However, the goal of playing FREELY, without effort, is attainable. This does not mean flubbing your way through things, nor does it preclude technique, training your ear, learning the music, or anything else. Rather, it is an additive approach that produces a unique state of mind that comes with conscious practice that can then be sustained. Some call this being "in the zone." It's great to be there, but what are the directions?
I work with many people across a number of disciplines; from actors to corporate executives who must speak in front of people, to other musicians. The key, ( even if only for a few minutes a day at first ) is to STOP TRYING and STOP THINKING ABOUT TRYING. What does this mean? It means supplanting the frustration of striving, or making mistakes with a very real commitment to freeing yourself enough to get out of your own way. How to do this? I work with a lot of techniques, depending upon the situation and the person I'm with, but a very good place to begin is the following:
ONE: Stand in front of your theremin, raise your arm and let it make a sound. Lower your arm. Do this ten times. It's easy right?.. .since all you are doing is raising your arm, you're utterly unconcerned with what to play. All that is required is that you make a noise. Insignificant as this sounds, when you are done, you will have had a very basic experience of pure effortlessness.
TWO: This technique requires that you be honest with yourself. Stand about ten feet from your theremin. Be patient and wait. Wait until you just feel RIGHT. Then walk up to the instrument and play -- NOT A SONG, NOT ANYTHING YOU KNOW. IMPROVISE MUSIC, even if it's just basic notes, but do not formalize anything into a scale. Play. BUT-- the second you find yourself THINKING about what comes next, or how you sound, STOP. It requires honesty to recognize and admit that you're trying, anticipating what to do next, planning, listening and judging. IT's crucial that you STOP when this happens. Move away again. Repeat this process at least a few times. You are seeking to familiarize yourself only with how it feels to play MINUS all the clutter, mindchatter, and preoccupation with perfection. It's easy to underestimate the value of doing this, UNTIL you've done it and actually had the genuine feeling of freely playing without TRYING.
Within the past month, I've used this technique ( or slight variations on it) with three people who've recently taken up the theremin. One of them has actually had a theremin for years and never been able to hold a melody. This seemed somewhat hard to believe, so I asked her to play Mary Had A Little Lamb... her assessment was right. She was so concerend with fingering and not committing to playing a note unless it was the right one, that she'd rendered herself incapable. After fifteen minutes of using this method, for the first time, she played a simple, straightforward melody of her own choosing. It just came out of her. Was it absolutely pitch perfect? Not really, but that didn't matter. She'd succeeded in getting out of her own way, she'd experienced the elation of playing freely FIRST, and thus was then able approach an actual song with far les