I generally like to write for a while, and then do character sheets. Sometimes, though, I get stuck on a plot or on a character. When that happens, it sometimes helps to think about real people.
One of the many interesting things about real people: The things they know and why they know them. I know a girl who giggles and flirts and does poorly in school. But she corrects the English teacher on who wrote which classic, and she can identify the painter of quite a few major works, because her parents love books and art.
Although real people don’t always stand stereotypes on their heads, it still surprises you what people know and why. I know how to change a tire because I thought I should. I know that the secret of representational art is to draw what you actually SEE, not what you know is there, because I took an adult class for fun. My grandmother taught me how to untangle yarn and jewelry chains. I used to know how to build macros in DOS because one of my nephews who was early into PCs told me I should.
Real people have whims, relatives, and imperatives outside your acquaintance. Real characters have the same, outside your narrative.
So, if you need for someone to know something, find out how and why they know it, and drop a little something about that earlier. The guy who untangles a delicate chain stayed with his grandmother a lot when he was a boy. The woman who safely eases a snake out of the way grew up in the country or volunteered at the zoo.
Remember that movie, THE POSEIDON ADVENTURE? Where the narrative group had to know how far underwater they had to go to get to safety? The fat old rich lady turned out to have been a champion underwater swimmer in her youth. Surprising but reasonable.
You know. People.
A WRITING PROMPT FOR YOU: Write down three things your character knows and why.