I think for the most part it’s just bruteforce. I do write kanji down a lot however, because I practice kanji drawing with this deck: Anki deck for Kanji drawing practice with all WaniKani kanji + jouyou + more
But I definitely abandoned WaniKani’s mnemonics for pronunciation very early on because I’m not a native English speaker so a lot of the time they would actually teach me a wrong reading (since in my accent a lot of these mnemonics simply don’t work).
Basically I just try to tell myself little stories involving those kanjis as I mentioned in my comment. As I progressed more I would focus on phonetic components that help guess and remember the reading of a good chunk of the kanji:
The more kanji you know the more these components are useful.