What comes first - the book or the movie?
As a Creative Director in advertising, I've learnt to think visually. As a result, I like to do a book storyboard using Googled photos - like this opening scene from The Smiting Texts. As the storyboard shows, I visualized a Hugh Laurie type as my witty British rogue Egyptologist Anson Hunter.
I did the same with the next books in the Egypt adventure series: "The Hathor Holocaust" "The Ibis Apocalypse" and the rest in the series.
This approach helps to achieve a heightened sense of reality - as important for the author in writing as it is to the reader living the story.
I've almost shot the movie BEFORE I've written the book.