There are a lot of different strategies for creating memorable characters. Some workshops will have you writing the characters entire life story before even beginning to write the novel or script. Some instructors will have you keep a journal that you write in every day, or week, as your character to get a feel for who they are and how they will respond to the situations that you put them in. All of this is great advise. If you have the time, do it. Get a composition note book for each character and write each day in their voice to get a feel for who they are. But some quick reminders for building characters-
Now that you have an idea of how to make better characters, get out there and write something amazing!