on Writers Helping Writers:

When writing a series, we need to adjust our writing techniques. Last year, we talked about the tricky balance of repeating information in a series from one book to another. We want to avoid giving readers a sense of déjà vu, but we also can’t assume that readers have read (or remember) previous books.
Similarly, if we hope readers of one book will be enticed to read the rest of the series, we may need to tweak our writing. Like the saying “similar but different,” books in a series need to be similar enough that readers who loved one book will find more of what they love in the other books, yet we also need to make the books different enough to not feel like reboots with just a few minor differences.
Today, let’s explore a few pointers to tempt readers into experiencing the rest of our series.