Not sure if this will help you or not because I don't make games or whatever, but I do write short stories from time to time, and it should work for any character regardless of gender.
Outline/write down everything about who you want them to be at the start.
Then start cataloging all the fine details. Approximate height, weight, build, age, job, car, hair color style and length, eye color, housing situation, personal history, relationships, hopes, dreams, asperations, etc. Even if only some of those things make it into your game/story it's good practice to really know and write down everything about your characters as reference material so you can look back at some point and be reminded of little things their birthdays or location of a scar/tattoo.
Then toss in some personality quicks, odd habits, anything that kinda sticks out a little, but is still close enough to normal that it's not weird.
Think about real people you know as inspiration for various traits.
Most folks aren't that clumsy, but we all know someone who trips or bumps into stuff contantly.
Or what about folks who fidget a lot? Those people who mindlessly just keep click click clicking all day with a pen while they concentrate on their work, or finger drum random songs all the time, stuff like that.
Maybe they live with their head in the clouds always daydreaming and are never fully attwntive to anything unless rushed or snapped back to reality.
Maybe they reallt hyper or lethargic?
A professional napper?
Total dog/cat enthusiast?
What about folks who talk incessantly. Yammering on and on for hours without actually saying anything at all. Or maybe a water cooler bro that's always gossiping anout everyone in the office? Or the sports nut who maybe played a little back in high school, but now all he talks about is how great/terrible the local teams are?
These aren't exactly normal behaviors everyone does so they stick out from the crowd enough to catch your attention, but they're still so commonplace that your readers will instantly see it and understand "Oh, he's kinda like that dude from accounting!"
And once you have all these little bits hammered out, written down, and filed away it should be easy enough to let them all mold together and form the personality and behavioral patterns of you characters. Then you can use it as a roadmap in the future to make sure they're always acting accordingly in any given situation.
Like I said before, may it or may mot help you, but it's pretty much how I build characters whenever I get the urge to do a little writing.