Playing from memory could be essential while performing in concert, festival or competition or even in exam.Knowing your piece by heart demonstrates that the composition has been studied in depth.
There are few ways to memorize music:How to begin?Listen recorded version of your piece first, so that you’ll have music in your ‘ear ‘already.Most of the people, not necessary musicians are able to remember songs and melodies quite easily by just listening it a couple of times. The same with pianists, they can memorize piece quite quickly by playing it through a few times. It is called aural memory, when musician knows how the music sounds in his head and when he is able to sing the piece through internally including dynamics and phrasing.The easiest way to memorize piece is repeat the same phrase over and over again, until its stays in your ear, then shift it to the succeeding phrase.Aural memory is one of the strongest and most reliable memory motivators.
The other step is to understand piece you are about to memorize intellectually.First pianist should know the main key and all upcoming modulating keys in the composition.Pupil should analyze the overall structure and know the cadential parts. Recognize repeating phrases and compare them with new material introduced in the piece. The whole process requires conscious control.This type of method is called intellectual or analytic memory.
The whole memorizing process requires lots of repetition, it involves constant finger action. Eventually fingers memorising patterns, this process is called kinaesthetic memory. Without aural and intellectual memory support finger memory wouldn’t be very reliable on its own.
The last method to memorise the music is visualy by remembering how the music looks on the page.
All the four: aural, analytic, kinaesthetic and visual methods should be maintained and combined simultaneously for effective memorizing process.
source: http://www.maestrolist.com/article/tips-on-how-to-memorise-your-piece.html
And also: http://musiced.about.com/od/adviceformusicians/a/memoryplaying.htm
Phil Tompkins: http://rmmpiano.tripod.com/memory.FAQ.html
in french: http://www.musicrea-jmc.fr/spip/Comment-travailler-une-oeuvre