These are techniques I collected from various piano forums.
From one member of PW:
1) Octave displacement: Practicing passages that are in the outer extremities of the piano in a more comfortable octave, and then moving them back to their original location. This was helpful when I was trying to master the final tremolo in the Prelude from Le Tombeau de Couperin by Ravel.
2) Random measure practice: Looking at the number of bars in the piece, and selecting a random number between 1 and that number, and practicing it. Being familiar with starting at almost anywhere in the piece speeds up and solidifies the memorization process.
3) Two-note slurs: I’ve found that in my zeal to emphasize the first note of a two-note slur, I often play a wimpy second note that doesn’t sound fully. To remedy this, I have found it is useful to pick a specific volume for the second note, practice it without the first note, and then play it is written.
4) Identifying what makes a section challenging and isolating the problematic spots: instead of trying to play through the entire passage in one fell swoop, it is better to pick two or three notes that are challenging, practice them slowly, and then put the passage back together.
5) Tapping the RH notes on the palm of the LH hand, or vice versa. This is helpful for discovering places where I’m using too much arm weight and pressing into the keys. Tapping out passages on wood surfaces is also a good idea – wood is a wonderful resonator. My teacher and I often do this and compare how her “taps” sound different than mine.
6) Slow practice.
7) Practicing without the pedal in pieces that require a perfect legato is a good way to check if the notes are smoothly connected.
8) Using a recording device and listening critically to one’s playing.
From another member of PW:
1. Memorizing the left hand alone.
2. Changing the rhythm of difficult passages from what is written to different rhythmic patterns. Similarly, changing the placement of the beat and off-beat.
3. Starting at random places in the piece - from memory.
4. Memorizing chord progressions or phrase-starting notes away from the piano.
5. Checking Youtube to verify that I am reading the piece correctly - note-wise and rhythm-wise. Then staying away from Youtube until I've developed an interpretation.
6. Learning from Urtext, then, well into the process of learning, comparing my interpretation to a heavily edited version. I usually stick with my ideas, but it is an interesting exercise.
7. Asking my teacher where the difficult places are and learning those first, very, very slowly.
8. Learning the piece from the beginning and from the end and working towards the middle.
9. Practicing with no pedals.
10. Practicing in my head, sans piano.