Article found here on SUPERHERO NATION.
1. Find a list of character traits. I would recommend using the list from SN, there's plenty of them, trust me. Or if you want something more visual...
2. Now choose a couple of traits that are noticeable in your character(s). It can be two positive traits and one negative traits, or two positive and negative traits, or two negative traits and one positive trait. Just make sure your character has at least one positive and negative trait. No one can be perfect or that bad either. Plus it makes your readers want to connect to your character if they find traits that are like theirs, if that makes sense.
3. Now ask yourself why your character is like the traits you chose out for him/her.
So, why?
It's probably a bit more helpful if you read the original
article, because it might make a bit more sense.
Also don't forget to fill out a character questionnaire, that can be found
here. I would suggest just filling out the first five questions, so you can know what your character would look like. But you can do all of them, if you want to.
Also, you don't have to use that questionnaire, there are others out there in the world. That was just one that I remembered at the moment.