Character development should be the one of the first things we do when we begin to write a manuscript. To start, I like want to know what era I'm writing in. It helps to know if I'm in the country or the city. Then I can go with the face of the characters and their body type.
The book I have just finished, and am now re-writing, is set in 1804 in the mountains of Tennessee. Tennessee is a new state and the area is beginning to be settled. Susannah, the main character is a spoiled woman. Her family is wealthy and she has everything she ever wanted. She also spouts off and hurts feelings. She is about 5'5" tall, black curly hair, and brown eyes. Her complexion is very fair. Her clothes are the best she can fine and she likes to brag about them. During the story, she changes. In fact it begins in the second chapter. She will turn into a generous, pleasant person. She is going to turn out to be someone we will all love and like to be around.
The male main character is Dr. Valentine Minor. He's a doctor and is practicing in the area. He is tall, dark complexion, almost black eyes. He is very humble. He loves what he does and he works endlessly with his patients in the mountains. His clothes are not the finest, in fact they are wearing out. Money does not come easily, but food is given in payment for his services.
There are several ways to keep records of your characters. I use a notebook. Susan Page Davis uses index cards. There is also a sheet you can find on the internet with one hundred character details. That takes a long time to do, but you know your character well when you've finished.
We should try to make our characters as believable as possible. Remember the time you are writing about. I would not have Susannah with a short hair style. It has to be long because no woman would be seen with short hair.The only time it would have been cut would be if they had lice.
Remember as you write the book, you'll have to refer to those notebooks or cards. It is so easy to forget what someone looked like. I've had to do that many times.
Tell me how you keep up with your characters.