Have you ever sat down and prepared an outline that describes your characters? Thought about their likes/dislikes? Where they’ve been and what types of things they like to do?
Try creating such a list for each character in your story, whether a main character or a subordinate. Include where they are from, family ties, mannerisms (such as head toss, twiddling fingers) and friends.
Write out some sample dialogue. Do your characters speak with an accent? Use contractions or use more formal language?
Even look through websites and find a picture of where your characters live, how they dress, places they might visit.
Put all this in a binder so that it is easy to access.
Now, begin working on your characters!