Series Are Not for Everyone
There are pitfalls to writing a series:
If you’re traditionally published and book one doesn’t sell, you may find your contract cancelled, or you could find yourself contractually obliged to write the second or third book of a series that has no reader base. That time could be better spent writing something new.
You might want to continue the series, but the publisher loses interest due to poor sales. (Remember however, poor sales can often be more of a reflection of poor marketing.)
You might fall out of love with your series. Writing for the same characters and situations can take its toll and there’s a possibility that you will lose interest.
If you are someone who likes new shiny plot lines with new protagonists and have a list of 100 books you want to write, you will have to really dig deep and focus if you want to start, and more importantly finish, a series.
Each book will need to work as a story in its own right. Writers have been known to simply split their books into three in order to offer a trilogy. Some will end on a cliffhanger that will assume the reader will buy book two, or worse; wait a year for the next instalment. This can frustrate the reader, who wants a complete reading experience with each book. There is a skill to creating a trilogy or a series where each part is its own story.
Planning an epic novel? Don’t write a 200,000 word book. Break it into a three-part series. The key is to think of satisfying endings for the reader for each book, and also to leave them wanting more.