I divide misgendering into two categories:
1. Accidental
2. Deliberate
When someone misgenders me, I make a determination in my head: Is it accidental or deliberate.
If it's accidental, I remind them that I'm female in a low key way "Please call me ma'am", or "Please use 'she'" or something like that. If they get defensive I assure them I know they didn't do it on purpose, but I repeat my request.
If it's deliberate, then that's a microagression. First time someone does it, I correct them assertively, as I would if it were accidental, but if it persists, I treat it as I would any other mean-spirited insult.