Then when I get to a point where I can no longer keep calling my characters "the man", "the woman", "the teenager", etc. I give them names. But still, I don't know my character, I don't have them all fleshed out until I've gotten into writing the first draft of my story. Then I gradually come up with my character's backstory as necessary. Maybe I come up with a great twist in their past for future reference. But as I write the story I meet them and get to know them as I would a normal person.
I do the plot, then the character.
I agreed with those who said that “There is no right or wrong way.” The only way that suits you. The last time I try to write a list of characters with names, descriptions of their appearance, age, race, nationality, language, favourite countries (if they are travelling), job or another source of money, and so on. Sometimes, I use a little part of those descriptions in my chapters. Usually, I can put these descriptions in the first chapters or chapters where new characters come into the scene. For example, if you would look at the first chapter of “C'est dangereux”, my French story, you would find these descriptions in the very beginning. They are from this list. I can't write any story without this list. I think that film producers work in the same way.
But the way to accumulate information about characters it is not about creating characters as such. The form of characters depends on the story's genre. If you write a romance novel, your characters had to be romantic, lovable, and, as far as I recommend, beautiful and young. But there is no exact rules or dogmas: you can write something like “Sex and the City” if you make them older than just young ones. If you write a detective novel, they had to be any age, but usually older, strong ones and being those who understand unfamiliar people. Women in detective novels, if they are detectives, can be strong ones, too.
If your character is a terrorist, he is a man, the next, serves in the army of some country, a former military man who doesn't like the country or politicians. He is 60 something if he is a general (I mean the boss), and 20 or 30 something if he is a common soldier of some terrorist company. If your characters are living in a fantasy genre, vampires' story, then the rules are changing. The main thing it is not a way to accumulate information about characters; the main thing is to understand why you need this character in a particular story.