First, you have to simply not care if you sit down and you go completely blank. You are not Horowitz so why anyone does at this level really means nothing. (unless some up-an-coming virtuoso shows up)
One thing I have found tremendously distracting is playing memorized music on strange pianos in different settings. In my own home, if I change the lighting, it increases memorization errors. Try to play on strange pianos. In showrooms. Friends' homes. I've even thought it would be good to check out and play interesting pianos on Craigslist - theoretically you might buy one if it was really nice, right?
As far as being perfect, when you perform, you have to forget about that and play from your heart and create your illusion. I know one pianist in particular who get's his wrong notes "wholesale" that plays at rag time festivals on the West Coast that is exquisite to listen too - my favorite of the entire festival and there are rag time virtuosos there too. Remember than Anton Rubenstein said something to effect, I could compose a concerto with my wrong notes.
So get over wrong notes.
Further, it is also my opinion that you DO NOT reduce speed to main accuracy. There is nothing more boring than some journeyman "performance" of some piece (Gershwin's Preludes are great example) that is played slow like a beginner. (I do acknowledge that you could place Flight of the Bumblebee like some serene Debussy which would be art - that is OK and I'm all for it.) But if he piece demands fire and speed, give it that. Remember, accuracy is not was stiffs the soul - emotion does - so play it the way you want to, not the way you can.
MEMORIZING: (If your memory is absolute, skip this)
Memorizing, if difficult is perhaps the major obstacle - especially if you go blank which I have done in the middle of a performance - luckily it was a cadenza and I simply forgot how to start it. So who knows how long I paused. I know he organist (it was a duet) looked at me in terror (!) but I just resumed where the cadenza finished.
Josh Wright has good pointer to organize the piece in sections you can play in any order. Practice playing the sections in reverse order. What is nice about sections is they give you many places to resume if you get lost. If you don't have seconds, and you forget how to start the piece, well, your only recover is to start playing something else that is startable.
When I've blown a piece, sometimes I just start playing something else. Frankly, friends and family probably don't know the difference. There is a Chopin Etude or Prelude that climaxes into a Rachmaninov theme that will blow the roof off the joint.
CONCLUSION
I think the biggest problem is the distraction of Strange Piano and Setting AND YOUR CLOTHING! These can sabotage your memorization which is the bedrock of your performance.
Second is throw accuracy under the bus for speed and interpretation. Even the great ones hit wrong notes.
CLOTHING:
If you are going to perform in a suit (or
?), get used to it. I would also say have fun with your clothes. Yuja Want says she doesn't dress provocatively, but really folks! I've seen guys playing sleeveless which is actually a great way. Lang Lang played a late night talk show I think in all black t-shirt and possibly black jeans. Keith Jarrett was uber casual.
Topic: Amateur Competitions