Think of times of the day when there is less stress, fewer tasks to attend and if you know you won’t be mad at friends and family. At those moments you have to focus your attention on music. Smaller music fragments can also be further expanded in musical form. Those measures 2-4 may eventually become a full heading for exposure, transition, development or transition. As your memory improves the piece, you can consider those larger sections as smaller fragments of the general piece of music. Using the elements of music theory to enhance your memorization practice is actually a two-edged strategy.
I try not to get depressed and go back to the song and keep working. I learned to work on very small pieces at the same time. Sometimes just a note to improve the ability to learn, play relaxed and remember. Many methods of classical pianism continue to emphasize pure repetition in the development of musical memorization, which works well if you have to practice four to eight hours a day.
Most lyrics tell a kind of story and if you can “connect” parts of the music you play with parts of the story being sung, it becomes much easier to remember. When I play instrumental songs, I make up my own story in my head and link parts of the music to that story that plays in my head. It’s kind of complicated, but once you’ve mastered it, it’s a great way to quickly memorize a lot of songs.
These starting places must be indicated on your score. You can mark them with A, B, C, etc., or 1, 2, 3, etc. Try to number the piece back from start to start so that you count down instead of up. Another system I learned from an excellent pianist is to mark the starting places using circulating S (to display the “starting place”). In his method he creates a hierarchy of starting places.
For example, start with a short section with measurements and lines. Remember each individual size of a line and add them from the last, such as making building blocks one by one and then mounting them. If you have that (and accurate!), add the previous one and then the previous one until I get back to the beginning. Maybe it can start in the middle of the piece, or seven steps in. This is called a playground and it is a great way to challenge yourself to memorize and measure them all thoroughly. Too often pianists get stuck with top-down pieces.
I could play it out of my head, but I couldn’t imagine it with enough detail to recover from a slip. By remembering first, you ensure that your understanding shaggy of music is not just muscle memory or just humming the melody. It is a mental image of every note in the piece in its musical context.