Okay, I got a some really great advice the other day (for the life of me, I can’t remember where).
When you finish a book and you are working on a sequel to it, it was recommended that you writing little “in-between” stories with your characters to keep your readers from losing interest in the series. I’m avidly considering doing so with mine. They would be simple, maybe 2,000 word shorts of “a day in the life” of one of your characters or a group of them. You could even use them as a prologue to your next book! How exciting!
I’m so interested to see if any authors I know have done this. Though I do know that Robert Jordan did that after the 11th book in his series just before he died in 2007. He came out with a prequel to his series centered on two of the characters from the story, called “New Spring.” It really angered a lot of his fans, though, (including me!) who wanted to read the promised conclusion to the epic series, not a back-story.
So, with regards to that terrible idea from my favorite author, I recommend “in-betweeners” or prequels only if you have a smaller fan base.