Create a list of questions, or download a template questionnaire from the Internet.
Answer the basic questions about your character -- age, sex, martial status, whether they have children, and where they work.
Begin to write their feelings about these sitations. Are they happily married? Are they faithful to their spouse? Do they love their children? Do they enjoy their job? Provide at least a one-line answer for all of these questions.
Continue through the list you downloaded, or simply begin asking more personal and historical questions of the character. What is their family history? Do they have a family secret they are keeping? Why did they leave home, or why didn't they?
Provide as many answers as you are willing and able to. You will discover at the end of the exercise, you will have a fuller, more-balanced character history. The answers to the questions will guide you in your writing. You will know your character more, and thus should have an easier time writing about them.