I have had tremors for all of my 61 years. When I was in music school, I couldn't even play in a lesson.
Then, when I was venting my frustration over having folded during my senior jury, a fellow classmate said: why don't you take Inderal? He said that all of the musicians in Europe take it, and it is prescribed for stage fright.
To cut to the chase, I actually started laughing during my next jury because the nerves monkey was off of my back forever.
So, for the short term, have your Doctor write you a prescription for this very common non-narcotic beta blocker. It is available generically, and it is cheap.
What it does is to temporarily restrict your adrenal glands, which is what happens when you get nervous. Your body starts pumping tons of insulin into your bloodstream, and for the time being, the tremors are irreversible, regardless of any "good thoughts" you might conjure up.
Unlike Valium or Xanax, Inderal does not effect your mind and cause memory slips.
Second, I underwent Neurofeedback training a few years ago, and it has made a permanent change in my nervous system. It is expensive, but a study out of the Royal Conservatory in London showed a 40% improvement in performance among piano majors.
Finally, there is a cardiac breathing biofeedback program called Heartmath, which I do every day for five minutes. It is a recommended follow-up to Neurofeedback. After awhile, you can "zone in" on your breathing at will.
So, put a big smile on your face because you are now on the road to getting rid of your nerve problems once and for all. Your Doctor will have you start out with a small dosage, and then you have to see what is the right amount for your particular body. Also, you have to see how much time ahead of your playing that you should take it before it takes effect.
Good luck to you.