First and foremost – all series are genre-less. It isn’t a genre but a collection of books within a genre – be it romance, western, fantasy, science fiction, non-fiction, horror or whatever. I can probably name at least one series in almost any specific genre. Western: Zane Grey’s “Triology” consisting of Betty Zane, The Last Trail, and The Spirit of the Border. Science Fiction? Orson Scott Card’s “Ender’s Shadow” Series with Ender’s Shadow, Shadow of the Hegemon, Shadow Puppets and Shadow of the Giant. I can even get a little more specific with a tighter genre that includes two sub-categories. How about Amish Historical Romance? Murray Pura’s “Snapshots in History” which includes The Wings of Morning, The Face of Heaven and Whispers Of A New Dawn.
My friend, Elyse Salpeter just released book 2 of her “The Children of Demilee” series. The first book is The World of Karov. Her new book is The Ruby Amulet. What genre is this series? Offhand I’d call it fantasy, YA with a touch of darkness. Check it out at Amazon.com for the ebook version It is also available in paperback.
I currently have a co-author (Jack Franklin) for a series and our first book of “The Vamazonian Chronicles” is available with the title of Ancient Blood: The Amazon. It is available at Amazon.com in both paperback and ebook versions. It is also available at B&N, Damnation Books and your local bookstores. It is the first in a planned six book series that has been outlined. Book 2 (Ancient Blood: The Homeland) is currently undergoing final edits.
Second. There are two approaches to a series. You can write one long epic tale (think Lord of the Rings) where it is broken at a point that satisfies but also leaves the reader wanting more. The other method is to write a complete story in one book but have a thread that will continue into the next book and the one after that. Actually, Lord of the Rings has a thread working through all three books but the difference is – a reader can’t pick up book 2 (The Two Towers) and finish it and be contented. The reader needs to know the beginning and find a conclusion.
In our Vamazonian Chronicles, each novel is a complete tale but the continuing thread gets addressed but not resolved. It is possible for a reader to pick up any of the books and have a satisfying tale with an ending. The underlying thread is not answered but the story is done until the next book.
Sometimes the series is even simpler. It is a group of books, each a complete story, with one main character. or locale. Series needn't be long tales. I read a book of three short stories. Each story took place in the same house. The stories involved the original owner, another set of owners and finally, the current owner. I found the stories a delight to read and also how easily the author had woven the tales together, linking each new story back to the previous tales. Sometimes a series can be recognized by the title alone such as those written by Denise Vitola: Opalite Moon, Quantum Moon,M and Manjinn Moon.
As noted earlier, series can be written by a single author, co-written by two authors, or even a collection of three or more authors.
To make it very simple. Series are just books which most people find easier to read in the sequence in which they are written. There's really no secret or mystery behind a series. It is just the ability to tell a continuing tale while not boring the reader.