When you see sales dip in your current book and you want to default to stress and last minute campaigns to try to boost sales, I want you to remember something key.
Writing your next book sells your current one.
Let me explain.
Trying to track trends the way you would with standard e-commerce doesn't really work for books. Trying to identify peak buying season is even harder. I remember August 2023 being one of my best sales months to date, and I have no idea why. (I assume summer? But who knows?) Sure, you can understand that Romantasy books with dragons are popular, but it's very hard to be more specific than that, and even then, it's not a guarantee that your book would have the same success if you include those things. I suspect it's got something to do with fantasy authors being such an over saturated market. I read somewhere once that in the USA alone there are over 2 million of us and it's hard to get concrete data together about our indie industry.
That's why it all comes back to marketing. Nothing will help you market your book more than building out your backlist and having a variety of your own books to market. Writing this post, I realised aside from the odd two week holiday here or there, I've been writing solidly since mid 2022 trying to do exactly that and I still get a thrill when I see older copies of my books sell while I'm working on the more recent releases.
This is not to say you shouldn't do a special edition, or other incentives for your readers. If this is your thing, please do it! In fact, if you can, I would encourage it, because it's a great marketing tactic. But when you're done, get back to writing book 2, and book 3. Because at the end of the day these are the things that are going to help you reach the sales you had hoped to see.