There are two important questions you should answer when creating a character; two for the antagonist and the same two for the protagonist. Answers to these questions dictate how your characters will behave and under what motivations they make decisions.
Don’t structure your characters on the fly. Decide on clothing, environment, and speech patterns as a support for their personalities, but remember, a character is created through behaviors—not your descriptions. For example, think of the behavior Atticus Finch exhibits in the movie version of To Kill a Mockingbird. You can tell he’s a man of integrity and caring when he takes a bag full of nuts as payment for his legal fee. He corrects his daughter’s behavior by encouraging her to be tolerant of those who were hit by the Depression and their need for dignity. The reader makes the conclusions about Atticus without the writer saying so.
Here are the questions: 1) What is the character’s tangible objective in the story? In other words, what is the one thing the character wants more than anything else, and have one–just one–overriding goal. 2) According to the character’s backstory, what is the character’s primary motivation for wanting that goal? The character has to have a strong reason (motivation) for putting him or her self in jeopardy to achieve it.
Here’s an unrelated tip: Characters should not sound the same. Readers should be able to know who is talking by the way they talk. So, give them an identifiable pattern.