Have you ever noticed how keeping secrets or telling secrets sometimes get the best of people. Everyone loves to receive privileged information, and many times we love giving it away. So take advantage of our tendecy to be curious. Give your character a secret to keep or to divulge against his/her better judgment.
What will happen if Sue’s boss suspects she is falling in love with him? What about a teen-ager who joins a gang? How will his poor mother feel if she finds out? How does he keep her from finding out?
Secrets are great for causing suspense, and they can add another dimension to your character. How will your character hide his secret? What will be the fallout if he is found out?
Will giving your character a secret fear or desire broaden the story? Was there something degrading or shameful in his/her past that they choose to hide? Is there an aspect of their lives they want to keep a secret. Do they pretend to be someone they’re not?
He/She is your character. Build him/her any way you want. Give him/her a secret that will blow your readers away. Just go it!