Everyone else is sorta saying exactly what I'm thinking, so I guess here's my view. Make them complex, especially if they're main characters. Just make sure they're not one-dimensional unless they're a random side character. Though you can go outside the box and make a random character multi-dimensional. Give them flaws. Therefore, viewers can relate and even incorporate the character into their own life. Minor traits matter as well, and also ties in to being complex, multi-dimensional, and having flaws.