The jumping off point for these Wednesday's Tips is Writing The Fiction Series by Karen Wiesner.
Just as each story needs a road map to get from the beginning to the end, so does a series. Or does it? There are 2 kinds of series, the open end one and the closed end. Just what does this mean?
A closed end series is one when by the end of book three or four, the missing is found, the grail is in the hands of those seeking for it. Though each story is complete in itself there are larger problems to be solved. Fantasy series often follow this story. Lord of The Rings was written to be one story. Think of how long each of the three books was and consider having a book with all three in one. This book would have to be read with it resting on a hard surface like a desk. There are a lot of other series that fall into this pattern. The quest will continue but the underlying problem will remain. The reason the end of this series is closed becomes "there is some underlying reason for the quest and until the object is in the character or characters hands the story will continue." There are clues throughout the story that will lead you on to the next books.
Now for the open ended series. This series could go on forever since each story is complete and can be read without reading any other book in the series. Detective stories are often this kind since they are based on a single character who solves a crime, finds a murderer. Another series in open end is when there is a place involved or friendship. There may be references to the past books or appearances of the characters found in other books but the entire series doesn't need to be read for the stories to make sense.
If you've ever picked up a series book and read it. Starting in the middle of a closed end series will make things confusing. This happened to me several times while judging contests. The middle story was a contestant and frankly the story made no sense. Not having read the first or second story in the series I was in an uncharted area and other than the writing I found the third or fourth book hard to judge. The open end series gave me no problem in the judging since there was no need to read the other books before I read book 4 or 5.