There are many exercises designed to develop your left hand. If your piano teacher does not tell you which ones (they really should), here's some information:
Beginner & intermediate: Here is an amazing list of Czerny Etudes scores with their descriptions for your needs: https://pianoexercises.org/exercises/czerny/. Op. 399 and Op. 718 are specifically for the left hand, whilst the other etudes tend to split the hands and give both a workout!
Intermediate/Advanced: Chopin Etude: Op. 25 No. 7. I love this etude... it's SO nostalgic.
Advanced: Some examples are Chopin: Etude Op. 10 No. 4 and Op. 25 No. 12.
SELECT PIECES WITH AN ACTIVE LEFT HAND
Many normal pieces are also great for a strong left hand. You can pick passages from them to focus on. Some great examples are:
Beginner: Bach 2 and 3 Part Inventions; Clementi Sonatines
Intermediate: Sonatas by Clementi, Mozart & Haydn Sonatas.
Advanced: Beethoven Sonatas, Rachmaninoff Moment Musicaux Op. 16 No. 4 and Prelude Op. 23 No. 2.
PLAY LEFT HAND ONLY PIECES
There is a list of pieces here for the left hand and the scores are free: https://imslp.org/index.php?title=List_of_Piano_works_for_the_left_hand&oldid=764014
My favourites are: Intermediate/Advanced: Scriabin Prelude and Nocturne Op. 9 for the Left Hand.
Advanced: Blumenfeld Etude Op. 36.
DO SELECTIVE PRACTICING
Pick a difficult passage from a piece you are working on:
- Practice left hand alone, do rhythmic exercises from my instagram highlights.
- When you play, simply listen more to the left hand while you play slowly.
- Singing always help me hear the part of music I am trying the fix - so sing each hand while you play the other one.
Feel free to comment below your favourite left hand pieces!