Reddit reviews Performance Success: Performing Your Best Under Pressure (Theatre Arts)

My bassoon prof in my undergrad worked with Don Greene at Juilliard. He taught a performance anxiety class out of this book. Probably the biggest takeaway from it for me was a guided meditation that he refers to as centering that most people in the class found effective.

1. Know your music really well. If you're not prepared, it only gets harder under pressure.
   
2. Play as often as you can for absolutely everyone. Incorporate performing for random people into your practice. Grab someone from the hallway outside your practice room and say "Hey, can you listen to this?" Play for people so much that it becomes a boring routine, not a huge deal.
   
3. Practice playing under adverse conditions. Allard's students at the Paris conservatory were asked to run up and down flights of stairs before their lessons. Set a timer on your phone to go off at an unknown interval. Practice maintaining your focus and keep going anyway. My final exam for my performance anxiety class involved bubble soap and an airhorn. Tell people while you're performing for them to cough or drop a heavy book on the floor to distract you.

As a professional musician and teacher, I've been (and seen my students) in that situation many, many times and learned the hard way...First of all, you need to really learn about this "nervousness" , since this is perhaps a manifestation of something happening internally (lack of preparation, personality trait, etc.). One of the things that you gotta know is that everyone--in the performing world-- (no exception) experiences nervousness (fear response) at some extent (regardless of what they tell you or you think). Mr. "he looks so relaxed when he plays" learned how to manage his nerves and embrace them as a positive force. I know it sounds esoteric but it's not....Once you accept is gonna happen, you need to define why it's happening. Does this situation mimicks your everyday personality? is it lack of preparation? are the stakes to high (competitions, job audition, etc.)? Are the odds against you? etc., so you can start looking at the real source of the problem and hopefully, finding some answers...Next, find (specifically) how this "nervousness" manifests. Is it physical? (Sweaty hands? dry mouth? shaky arms? stiff neck, etc.) or mental? (voices in your head, inability to stay focused, overreacting at small mistakes?. If it's physical, you might want to ask your doctor if he can prescribe you some propanolol, a beta-blocker used widely by performing artists (I'm not gonna tell you how it works, look it up) please talk to your doctor first (DON'T GET ONE FROM YOU FRIENDS!!), since he can evaluate your health and tell you if it's right for you. I know the musicians community is divided about using beta-blockers but I can tell you from my own experience that it helped me a lot with sweaty hands (I play a string instrument).
The mental aspect is a little bit more difficult to tackle but not impossible. Chances are that you are trying to micro-manage every aspect of your performance (don't mess up that fingering, exaggerate dynamics here, release the tension in your elbow to get a smoother legato) and this stuff gets in the way of artistry. Here is where you have to make a big difference between practicing and performing (two complete different things). Leave that micro-managing stuff for the practice room (but don't do it too much either, it will drive you nuts). Finally, performing is a skill that you need to practice!!! you need to put yourself into "performing mode" often so you can learn how to "embrace your fear". Play for your peers, friends, parents, bf/gf, etc. No one around? use your imagination. I have a colleague that used to put (he probably still does) a lettuce head with a baseball cap and glasses in front of him to simulate an audience. You need to practice performing so you get to understand your own fears and insecurities...
Some books that might help:

A soprano on her head: http://www.amazon.com/Soprano-Her-Head-Right-Side-Up-Performances/dp/0911226214

The inner game of music:
http://www.amazon.com/gp/product/0385231261/ref=pd_lpo_k2_dp_sr_1?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=0911226214&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0TG9NP8HF8RR8017J1J2

-Performance success (or anything by Don Greene): http://www.amazon.com/Performance-Success-Performing-Pressure-Theatre/dp/0878301224/ref=sr_1_1?ie=UTF8&s=books&qid=1278682151&sr=1-1

I could write a lot more about this topic, but I have rehearsal; pm if you have more questions.