Piano (Memorization)

a.I use this method:1 - First, I read carefully the sheet music, trying to understand it structure and memorise it until I can write the music.2 - I listen the piece many times, played by a lot of good pianists, until I can sing it in my mind3 - I play the most dificult bar or phrase X times (when on can play the most dificult bar or phrase, all the others become quite easy)4 - After all this, I begin playing the first bar X times, then the 2º bar X times, then the 1º and 2º bars X times... This is the adictive method of learn. And each time I play a bar (or phrase), I sing it using the name of the keys.With this method, we never forgett, even many months later. And, during a recital, we do know, at each instant, what we are going to play many bars after.5 - Very important: to sleep well, after our daily practice. 

b.Don't memorize pieces by playing them. You must play the works of course, to solidify details and certain uncertainties like hand positions, and to distinguish the sound variation that you wish to hear between pitches and hands. But once you have the work firmly under your fingertips in terms of general perfection, you should make no effort to 'memorize it' by playing it through. Instead take the score away and work at it mentally, reading and understanding the details of the score. 

Memory should be natural, and when you finally do play by memory, you shouldn't make a single mistake. Unless you want to play pieces poorly, to play pieces well means to practice them so hard that memory does not become an issue anymore. 

However once you have the work solidified, I find I never need to revisit that piece much again - it's always there whenever you want to play it. (Aside from a little polishing and rereading) This is the way to build a large, strong repertoire.

c.muscle memory will almost always fail you in high pressure performance situations. you should have aural sense of the piece and not juse the 'put together' work, you should be able to  hear in your head individual lines 'isolated' away from the rest of whatever is going on. also hands separate memorization is key too. you should be able to work to play the piece from start to end with only a single hand and all the while 'hearing' the other hand in your head. my teacher recently assinged to me (and it has been adifficult assignment) to be able to sing a long the line that I'm not playing not just 'hear' it.   after than you should try to

play with both and in spots throughout, drop one hand, keep going with the other, add the other hand back in, then drop the other, etc etc.  you basically need to have such a detailed understanding of the score, form, harmony, counterpoint, etc. that you 'can't' play it incorrectly. this involves everything mentioned above.

also, letting your brain 'dwell' on your pieces when you are not practicing etiher is very important, at least for me it helps a bunch, i make sure daily, sometiimes multiple times per day, i listen to recordings of my pieces when i'm away from the piano both as 'background' while i do something else and actively, where i carefully listen to what is going on and trying to visualize the score and my hands as if i were playing.  also sitting and listenign wtih score in hand is good too. again i do this daily for months. by the time i need to play a piece by memory it is so secure (usually, if i have skipped some of this or just needed more time  maybe not so much) that even if i have a small bauble, it doesn't phase me, and even if a critical but unlikely concentration disaster occured, i can pick up and simply move /skip forward or back (rarely is this a good idea, usually try to start where you dropped it or just after it). and finish it out.