https://improvplanet.thinkific.com/
"The Four Pillars of Piano Technique" is now a full 32lesson course.
Enroll in at the link above.

1.Listen to nonpiano pieces by your composers:

Mozart Symphonies or Requiem. Or even just concerti.
Beethoven Symphonies or Hallelujah
Rachmaninoff Choral Music, Second Symphony
Grieg Holberg Suite
Schubert Art Songs (Lieder)
Brahms First Symphony

2. Practice transposing short bits
3. Copy music by hand
4. Transcribe short bits
5. "On every page of every piece, something new every day."
6. Write out a chord progression from your piece. Improvise and compose over it.
7. Discover an unknown composer:

Mozart Cimarosa, Galuppi, Dussek, Kozeluch, Hyacinth Jadin, Madame de Montegoult
Beethoven Clementi (sonatas, not sonatinas)
Bach Zelenka, JCF Fischer, Loeillet, Handel, Seixas, A Scarlatti, Chelleri, Platti, Rameau

8. Call B.S. on fingerings or motions that are not working.
9. Play along with your favorite recordings.
10. Write in your Zibaldone.