Set an Intention to memorize the music and plan to do only this memorization process for about 30 minutes
Focus on one measure (or very short phrase at a time) - no more than 5 or 6 notes!
Plan to only memorize no more than 4 or 5 measures in one sitting of about 30 minutes
Know how you will finger each note before beginning to memorize the measure
Do each of the following steps at least three times for each measure
Don't move on from one step to the next until you have mastered each step
Avoid shortcutting this process - Any shortcuts can result in short-circuited memories!
STEP 1 - Music - Focus on the music - Play while reading the music or, if learning by ear, while listening to the short section
STEP 2 - Hands - Focus on your hands - Play while looking at your hands (do not look at the music or listen to it!)
STEP 3 - Feel - Focus on the feel - Play without looking at your hands at all (For example, close your eyes!)
STEP 4 - Visualize - Focus on the memory - Play in your mind only. Don't actually play the measure just visualize your hands playing it.
Once you have memorized a few measures ...
Come back an hour later and play only the measures you memorized
Just before going to sleep that day, again, play only the measures you memorized. Sleep is very important to move short term memory into long term memory!
The next day, play the measures again a few times from memory before trying to memorize the next few measures of the tune.
Keep repeating this process each day or two until you have the whole tune memorized.
Remember to visualize (in your mind only) playing the measures you have memorized whenever and wherever you can. It's helpful to move your fingers/hands as you would if you were playing while doing this visualization work. See the link in the Additional Reading and Resources section below for a brief overview of the science of why visualization works so well.