Reviews
Amazon matters most, then Goodreads and BookBub. If you bought the audiobook, Audible reviews help too.
What you liked, who you'd hand it to, whether you'll read the next one. No summary needed; the blurb already does that.
While you're on Amazon, vote "helpful" on reviews you agree with. The top-voted reviews are the ones new readers see first.
Release news, sales, and free books. Pick one or both.