Unless the book is a stand alone I do this from the start. However I will admit I writer a lot of series. Now's the time to mention that I like my books in a series to be able to read on there own as well as together. I really enjoy writing series, but I want to make sure I'm consistent with descriptions of my characters and where they live. Keeping track of character features and issues is very important. A family tree and map of the town is helpful too. So all those character sheets I've done get assembled here in the order of how the books will be written and released.
Now I'm off to the next step. Coming?