In many cases, if you want to know about someone, you ask them questions and listen to their answers. Most people interview each other when they first meet. They get the basics, like names and professions. They may spur conversation with a compliment (love that necklace) or by mentioning an observation (sports/university logos on clothing, an accent).
And, if you have tuned your perceptions, you pay attention to the tone of the replies, the facial expressions, the hesitations, and the body language. You also take into account the context -- when and where you are asking and who else is around.
Interviewing characters is also a good way to get to know them. You can ask standard questions, and I've offered some "tell me about" interview prompts in a previous post. I'll add to that list here, but first I'd like to tie things up for the Bonding With Your Story's Characters series.
Throughout, I've said to know characters is to connect with them. In real life, you know people by what they do and say (and what they don't do and say). That means listening, watching, questioning, researching (through others and through artifacts, including online files), working with them and asking them questions.
If your subjects are actual living people, you probably can do all of these (with some exceptions for inaccessible celebrities). If your models are deceased, you can only research them.
If your characters are based on real people, they can be fictionalized, which may open up everything. It isn't unusual for me to end up listening to and observing my characters (whether I like it or not), and I understand this is common for a lot of fiction writers, once they get some understanding of their subjects. Working with characters was covered briefly in previous posts in this series. That takes an active suspension of disbelief and a developed and disciplined imagination.
If your characters are not based on real people, you can't research them directly, but you can dig into the lives of real people to get answers and examples. And then it is up to you to integrate them into the whole character in a credible way.
One thing I haven't mentioned yet is what the characters are thinking and what they are aware of. With real people, we may make assumptions about these, but we never really know what's going on in their minds. With fictional characters, the potential for absolute answers is there, and it is one of the joys of fiction to get perspectives that we can't access in real life.
Since I wrote the "tell me about" post two years ago, I've come up with some additional questions I value. Pick out a character, sit down with her in a coffee shop, and see if any of these questions get you anywhere:
What do you, character, need/want?
What is your biggest flaw (on the Seven Deadly Sins level)? When have you demonstrated it?
Why are you appealing? When have you demonstrated this?
Even if you don't know your family, what is your family role in the story? (This is especially valuable to find out when putting together characters for a series.)
What characterizes your connections (relationships) with others? (Collaborating? Provoking? Dominating? Helping? Organizing? Listening? Persuading?)
How powerful are you and how do you acquire and maintain power?
What characterizes your conflicts with others? (Or do you avoid conflict?)
What pushes you to the limit or triggers out-of-control or anti-social behavior? Have you experienced important traumas? Do you have acute sensitivities?
Tell me about your deepest secret(s).
What do you need to find out in the story?
What do you need to learn in the story?
Why are you distinctive?
• Magic (even if this is not fantasy or paranormal)
Why are you surprising?
What obligations do you think you have? What obligations do you actually have?
What is your work (and what are your attitudes toward work)?
What is your code of honor and what do you value?
That's the set of questions I'm using now to explore my characters. Sometimes, I fill out what I think the answers will be before I imagine meeting with the character. What I've discovered is they often will surprise me by what they know, what they don't know, and what I got wrong.