One of the most important aspects of memorization is pattern recognition.
Record this phrase on a tape recorder and play it back as you sleep.
Find patterns in music. Think of your theory, how does what you are playing relate to scales, chords, arpeggios, keys, time signatures, types of rhythm, hand positions, finger movements, etc.
Why think of:
C# D# E F# G# A B# C
When you can think:
that's a C# harmonic minor scale
Think of harmony, harmonic progressions and such.
Eg: Take the first phrase of Fur Elise. How many different chords are there amongst all the notes?
Only two, A minor and it's dominant 7th E major. Why try to remember the sequence of all those individual notes divided between the hands when you can use the two alternating chords to guide and focus your memorization.
Don't just play your pieces from one note to the next. Learn to analyze your pieces, on both the large and small scale. From sectional structures like sonata form, to phrasal structures such as melodic contour and line. Analyzing helps you develop your skills in pattern recognition.
Have solid fingering, and stick to it! Good fingering is extremely important, and when chosen well can help aid memorization. When you have a recurring note pattern, try to use the same fingering pattern as much as possible.
Here is an exercise:
Take a piano piece that is very easy for you and much under your present sill level, nothing with fancy technical stuff. Let's say Bach Minuet in G. Get the score, play it through until you are comfortable with it. Now transpose it into all 12 major keys at the keyboard. You are not allowed to write down your transpositions, only play from the original score. Try to use the same fingering through out, even if it seems twisty and weird - this will help you establish finger patterns.
Bonus - take the G major Minuet and transpose it into all 12 minor keys. Only work from original score, no writing stuff down. More bonus - transpose the Minuet into the 7 church modes for each of the 12 pitch classes.