Sometimes the story you want to tell is too big for a single book to cover. That’s when you need to create a series. To plan a series, you need to plan each book in advance. You can do this at the story treatment stage by writing down what needs to happen in the story.
You can adapt the story treatment idea to plan the story. Divide it by adventure and then drill down to plan each act in each book. The story treatment I detailed a week or so ago, is as follows: Idea. Log line. Act one, act two, act three, epilogue, scene descriptions.
You can adapt this to a series by repeating the above for each book in the series, until you complete the story arc. Act one in the story arc is the first book. The next act is the next few book and so on. If you need more acts, add them as books in the treatment. It’s not easy, but if done well, you will find you have a road map of your story arc.
Most series end after seven books, but you can continue for more books should you need them. The key is to have one adventure per book. If you plan it with care, you can create a series people will want to read. You do that by leaving your characters resting from one adventure with the next looming.
Of course there are other kinds of series, as well. These are books that can be read as stand alone stories but have the same characters. You can do these by planning each book on its own, using the same character charts. Be sure to add any additional information to the charts as you create them. Update your background materials with whatever changes each book brings to each character. That way, you know what you said in the last book and your readers won’t complain or worse, stop reading your books.
The driving force of this kind of series is characterization. You want your reader to want to spend more time with your characters. They must want to go with them on their adventures and see them safely through them.
In this instance you plan each book on its own. It’s not like the Lord of the Rings series or Harry Potter where each book builds on the one before. Though you can do that. Tolkien and Rawlings knew how their serial stories were going end from the first word in the first book.. You can do yours that way. Oor you can create a cast of characters. Add in some supporting characters and write any number of books with them. Cozy mysteries are good examples of this kind of series.
Whichever type of series you choose, plan them. You don’t have to outline each book in your series, if that’s not how you roll. But you do need to keep track of what you wrote, with regard to your characters. Keep that in mind and you will escape a world of hurt.