Ten Things to Help with Developing Characterizations
Colorizing: Decide your character's favorite color(s) and consider using it/them in some part of your setting where the character spends a great deal of time (like their home, their office, or their vehicle.) Avoid the usual paint/wallpaper/carpeting and go for more unusual expressions of color such as art, upholstery, ordinary objects and plants. If you need ideas, pick up paint chips and decorating pamphlets (usually free at your local home improvement store.)
Get Cooking: plan a meal that your character would prepare or order while out at a restaurant. Take into consideration their food likes/dislikes and whether they'd be daring and try something new or stick to traditional favorites. Get ideas from restaurant menus, cookbooks, cooking magazines and recipes you see on TV food shows. Keep in mind any applicable dietary requirements and seasonal favorites.
Horoscoping: Pick out a birth date for your character and read up on their astrological sign. Incorporate one of their sign's common traits into their habits, daily routines or personality. Learn how your character relates to other signs of the zodiac (astrological polar opposites are often great love interests.) If the sign doesn't seem to match your characterization, pick a different birth date and try again.
Inventorying: Imagine you're standing in front of your character's refrigerator, pantry, bathroom cabinet, tool chest or closet (or other place they keep stuff), and make a list of everything they keep in that place. Think about what your character would want to keep on hand, and why; also note if your character is neat, messy, nonchalant or has everything alphabetized or otherwise organized. Write up your character's next shopping list.
Journaling: Start a hand-written journal but write in character instead of with your own voice, and detail an event from your story through your character's eyes, emotions and opinions. If your character isn't the journaling type, write a letter, an e-mail or a text your character might send a friend about the story event.
Library Stocking: Decide what books your character enjoys reading and give them a supply (this can be anything from a couple paperbacks on the nightstand to a full formal library, depending on your character's situation.) If your character's favorites are part of your personal collection, pick up a book your character would love from the library or bookstore and read it.
Old Flaming: Work out a previous emotional relationship in which your character was involved (this can be anything from a close friendship to a marriage.) Write a timeline of the major events that happened in the relationship, if/when it ended, what reminds your character of that person in their life, and what your character brings to any new relationships as a result of the previous involvement.
Remembering Childhood: Write a one-page description of a significant event from your character's childhood. Think about how this event has affected them emotionally and/or physically from the time it happened to present date. Decide what part of their life (if any) it has permanently affected or changed. Create a sensory trigger for these memories (hearing a certain song, tasting a particular food, feeling a sensation on their skin, etc.) that always reminds the character of the event.
Schooling: Decide what kind of education (formal or otherwise) your character has experienced and how well they did in school or in the learning situation. Create at least one teacher or mentor who significantly influenced them in some way and invent a scenario in which the character thinks of this person. Write up the caption in your character's yearbook or create an educational memento that concisely illustrates the student they were (for example, 30 years after graduating, I still have the two medals I was awarded as a senior -- Creative Writing and Art -- in my jewelry box.)
Window Shopping: The next time you're at a mall or a department store and have some time to spare, look around and pick out an outfit for your character (you don't have to buy it) and write it into your story. Try to avoid designer brand name dropping and go more for describing the look, cut, fit, design, pattern and/or color. If your character's setting is not in the modern era, go to the library for books or check online for sites that show actual garments from history and put together one from that info. For those of you who are writing SF or non-Earth fantasy, try choosing a modern or historic garment that suits your character and then adapt it for your otherworldly setting.