So imagine this; the sun has gone down and there is a lull in the action. So your character goes home, walks into their room, and is all alone. It is still too early for bed, so what do they do next?
Often in novels, the only defining trait of characters is their occupation. A knight fights, trains, and does his other knightly duties…but nothing else. Even in YA books, the teen characters are said to be average teens, but many books have teens that seem to have no personality.
Does your character like to read books? Play video games? Do they play an instrument? Do they love crossword puzzles?
When you add in hobbies to characters, it adds way more depth into personality.
For example, a grim trenchcoat giantly muscled superhero might be more interesting if someone walked into his house and discovered he is a collector of ceramic cats. A stereotypical cheerleader might be more interesting if she is secretly obsessed with video games and even cosplays to conventions.
We all do something when we do not have something to do. So my question to you writers out there is what does your character do when they have nothing else to do? What hobby do they have that is not related to their job?