Some successful Indies are so prolific that they don't bother with ads. Their books are the ads. If you can release a book every 2-4 weeks, this could work.
It does work. It works for 6-8 weeks, where you pre-order the next book before the current one releases.
What also works is tying in your series with each other somehow.
At the end of my last book in series 1, there is 2 specific events.
My series 3 tied into providing 2 key people to the first event.
Series 5 starts with the second event from a previously unknown but hinted at perspective.
Series 4 was the sequel to series 1. 5 parallels 4, up until now 4 is paralleling 5.
Confused? Well, yes, but the result is new readers coming in anywhere are going back to the first series, and that converts very nicely. My book 1 still bounces in and out of the top 50k. And it's over 5 years old now.
My current aim is to get series 5 to the same place in the timeline as series 2, which is a spin off of 1, so I can get that series getting the love as well. And since I didn't document that actual timeline properly, I'm having to re-read series 2 to recreate it. But once I get both galxies back in sync time wise, then the real fun can begin.
