Supposedly having a great first book with serials either in the wings or already written is a strong enticement to publishers.
Typically, a serial is sequential, whereas the next book picks up some time after the previous book. Perhaps they don’t always connect to each other except for the main characters. But sometimes the story arc is big and runs through the whole collection.
When I was a young girl, I devoured the Nancy Drew books. Later I stumbled upon Roger Zelazney’s Chronicles of Amber series, and then later still Marion Zimmer Bradley’s Mists of Avalon books.
In the Avalon series, for the first time, I read a prequel that came after the first two sequential books in a series. I wasn’t sure I liked that, but after I read it, the rest of the story I already knew became more organized in my mind and I decided it wasn’t so bad, after all.
My own book Symbiosis is evolving as part of a series, but this story isn’t being told in a sequential sort of way. Rather, the first book lays some groundwork and introduces a concept. The next book isn’t before or after, but simultaneously happening, and in a different realm. It depicts a small part of the big picture. There is an overlap with a minor character that features in both (and this character will likely feature in all of the ones still waiting in the ethers, too).
The stories tie together but not in an overt way, and each story stands on its own. But to see the whole picture, all of them would be needed.
I guess my question is, do I wait to market the first until the others are done, or once I’m finished editing the first, should I go forward with it while working on the others? To wait would mean a fairly long wait.