Speaking as someone who plays OCs and also published a novel (self-pubbed, but hey, I had to create all the characters in it) ... I tend to come up with a character's primary interest, and then think of what might conflict with that interest.

Some examples: My current tabletop character is a centaur who dreams of being a famous actress, but keeps getting cast as the horse. I thought, "Okay, what centaur wants to be an actress? What's her beauty routine like? Does she have a wish list of dream roles she's been denied? Is she angry at her director? Angry enough to frame him for murrrrderrr?"

My novel's main character is a teenage girl who's a good student and varsity athlete, but also loves trashy romance novels and wants to be taken seriously as a sexual being. Those two traits conflict when she dates a vampire who wants her to derail her life for him.

I feel like I'm not explaining very well, but that's my formula. 1) Give the character an interest or a drive. 2) Are they free to pursue it? What obstacles do they run into (internal obstacles count)? 3) What does a person in those circumstances act like?

World-building comes ...... close to last for me. Not saying that's good, but I do think nailing down what propels a character internally makes it easier to find hooks for them to interact with others.