My strategy (with only a one-time exception) has always been to only have reduced price or free promotions of the first novel in my several series. The logic, of course, being that my profit comes from sell-through so I should not reduce the price on those. And I fear that people will not buy the others counting on them soon also being free or reduced price.
However, this obviously limits the number of novels I can run a promotion on. So what do the rest of you do and what is your strategy? Do you do reduced price promotions on 2nd, 3rd, 4th novels in your series? Does it seem to work well for you? Or do you not? Or have some other strategy I'm not thinking of?
Edit: In the Bookbub thread Jeff brought up Wayne Stinnett. I was thinking of him when I made this post. He had a system by which he applied for BB promotion one after another for his entire catalog. I just did a little checking and just going by observation, he is still very active and had at least three BB promotions in 2021. I suppose he is still using the same strategy although I didn't look at which novels in a series he was promoting.