There is a lot of vocab that include the kanji for person. 人. And each has it’s own reading. This method has been a fast and easy way to never forget the right reading.
You may notice in the early lessons that にん is the reading used when talking about amounts of people (beyond 2).
I found that associating the にん reading with large quantities of people and the じん reading with low quantities of people I could always remember which reading to use through mnemonics.
For example:
びょうにん means patient or sick person. Well there are plenty of patients out there!
たにん means other person. There are lots of other people out there besides myself.
あくにん lots of “villians” in the world
めいじん most people don’t make it to be a “famous person”
しゅじん only one “head of household” per household
べつじん very few are able to change their ways and become a “different person”
さつじん everyone dies but only a few die by “murder”
As for むらびと which means villager. Well I just think of villagers as being weird people who would rather identify themselves as びと
I find that most cases of じん refer to a personality characteristic or something otherwise permanent, while にん refers to an occupation or temporary status.
This covers a pretty big majority of words automatically. Then for ones that blur the line I make up mnemonics based on that principle (for example villain/あくにん is a temporary occupation because i’m going to redeem them to the side of good, whereupon they’ll be a changed person/べつじん because they have a new personality).
