On our refrigerator at home there is a white board. The type you write on with dry erase markers. It is supposed to be for communications between family members. Little notes for reminders, grocery lists, etc. But being my family there are notes on it like a strange drawing of a cat wit the word "Sodium, Sodium, Sodium, Sodium, CATMAN" next to it. An old note that started with "Can anyone help with..", now ends with "the tinfoil hats." Another little drawing of an odd man that someone wrote "WINNINNNNNNG!" next to.
You now have a good idea into the mindset of my family.
When writers come up with characters, it is easy to end with the person. Once you come up with how they look, throw a few idiosyncrasies, you might think that you are done with the character. Not thinking how that person's environment can expand their personality. Do they live in an apartment? A house? Do they spend more time in their car? Do they have a car? What is in their purse? Their wallet?
Something as simple as a favorite item can give you great insight into the mind of the character. What does their favorite shirt say about them? Is it a threadbare T-shirt with a heavy metal band's logo on it? Is it a tailored shirt they think is lucky? A sweatshirt they only wear at home when they are relaxing?
An object or a person's home can tell you more about them then a paragraph explaining their personality.
Terry Pratchett did this wonderfully in Unseen Academicals. He spends a few pages describing the beds of the main characters. Not only does it give you an idea about their personalities, he gives you a few tidbits that seem to contradict themselves. As you get further into the story, the contradictions are what makes those characters interesting.
Going back the the white board on my fridge. Could you tell we have artists in the house? We have geek level of humor.* And that we don't organize every level of our life. That what the board was bought for, but never used that way. That one object let you find out more about my family, than me writing about each of our personalities.
Remember your characters interact with a world, one that they cannot help but to shape. Let your readers have those little glimpses, they round out a character.
*Sodium, Sodium, Sodium, Sodium, CATMAN can be written as Na, Na, Na, Na, Catman! Hopefully you get it now.