I'm currently writing the 10th book in my ARKANE thriller series, so I am revisiting the little details that make my characters consistent across the books. I have forgotten so much since End of Days!
Here are some of the things to think about for continuation across series. Watch the video below or here on YouTube.
In the video, I go through:
(1) Continuation of character history, physical and personality traits
(2) How much to repeat in case people don't start with the first book
(3) What I remember vs what I actually wrote
(4) A story in itself but also part of a series
(5) Does the protagonist change within the book or over a series of books?
(6) How to cope with timescale over multiple books
(7) Retrofitting cover design and branding
You can find my series fiction here: https://jfpenn.com/fiction/
Get your free 7 Steps to Write your Novel cheatsheet at: http://www.thecreativepenn.com/7steps