I took an online creative writing class that took a short time to finish, unfortunately I don't remember where you culd find it if you're interested in it (it was free). The writing assignments were fun to do although it took a while. You would describe a lot about your character. I had to describe the characters family, friends, where this character went to school, where they feel comfortable at what their fears are. I had to describe what their rooms were like if they had movies or books or a diary hidden somewhere. What their ethnicities are and what they celebrate. I also had to mention something that they don't know about themselves. Their secret weaknesses and strengths. Some people have problems making their character believable. An exercise given to me by the same online writing class said to 'observe' people try to make up stories of each person may you be at the gracery store or a park. Pay attention to what they're getting or who they have with them. Another way to add a beleiveable character is think of two people you know and mash up thier personalites or change their gender. Like knowing someone to have a quiter personality than another person you may know. I know some writers make characters that are similar to themselves, so if you want to add something different this is a good thing to try. You can think about how your character will respond if they were put into different situations. If your character has a gun pointed at them or if a random stranger is in danger or a simple animal is in danger. Maybe the character is in an interview, pretend you're the interviewer. Hopefully this helps with developing a character and that you didn't hear at least one of these things.