Depending on what you are learning there will be specific strategies that can assist you in learning the passages, this is where a good teacher comes in handy or good specific questions asked and your personal challenge with the issue presented neatly online may yield better ideas than random advice on practicing as a whole.
I've been self-taught since 14 years old and have been playing since age 10. I'm 16 so I've been playing for 6 years I guess lol (i probs mentioned this earlier but i felt it was necessary to say again)
well the sonatas i feel would be most possible for me to learn before im 18 that i would be interested in being able to play to a masterful extent would be the following:
czerny's 9th piano sonata in b minor
schubert's piano sonata in a minor (d845)
mozart's piano sonata in a minor
grieg's piano sonata in e minor
rachmaninoff's piano sonata in d and b flat minor
schumann (both clara and robert)'s piano sonatas in g minor
robert schumann's piano sonata in f sharp minor
all of faure's nocturnes and barcaroles
haydn's piano sonata in b, e, and g minor
beethoven's pathetique or appasionata. maybe even the hammerklavier.
the pieces i know how to play are:
mozart's fantasies in d and c minor
bach's bwv910, 923, some of the well tempered clavier preludes and fugues, his sinfonia in f minor, and a few more bach pieces
the first mov of beethoven's moonlight sonata. i attempted to learn the finale but i felt it was too much for me lmao
wagner fantasy in f sharp minor (the first mov)
fur elise
mozart adagio in b minor
chopin nocturne in f minor and f sharp minor
chopin polonaise in c minor
brahms intermezzo in e minor
if you guys think im not ready for the pieces i said i was interested in learning based on my repretoire then feel free to recommend me a sonata or suite in a minor key. ive always been biased to minor keys so i would like my first fully learned sonata to be in a minor key as well. thanks in advance.