Look at the characters you like in other media and take inspiration from them! Also I suggest giving them a story or at least some kind of goal, motivation, fear and flaws. If they’re flat you’re most likely to lose interest in them.

Also Try giving them unique/unpredictable traits. Makes for a more interesting character! I find if I give them a lot of predictable traits the more detached and bored I am of them. like for example a shy girl who’s quiet, clumsy, is a book worm and wears pastel colors is typical and boring, but adding one or two unpredictable traits like she secretly is a metal head and goes crazy at concerts kinda spices things up a little!