Here are my thoughts on 3 kinds of stories. So, for those who don’t know:
Prequel: takes place before the established story
Sequel: follow-up to the established story
Companion: not necessarily a prequel or sequel, but may include characters or theme found in the established story.
I’m going to use my books as examples here (obviously).
There was a time when I wasn’t crazy about “prequels”. Especially if I wasn’t aware that’s what I was reading or watching. Later, I realized, prequels can come in handy. They can help establish certain character’s roles, or even answer questions presented in the established story. Even though I wrote it as a companion story, Allan and Mac can also be considered, a prequel. It introduces characters and events that later become important in the Valentine series. For example, it answers the question of who is watching Val and her friends from over the Grand Central at the end of The Patron Saint.
Then, there’s the sequel. A good story deserves a good follow-up. I prefer to have the second leg of the story pick up where the first one left off. Some writers like to throw in a flash back, or a preface, to explain things to anyone who may not be familiar with the first story. I’m going to be honest here: most of the time, when I read a story that is a sequel to another story, I usually skip the preface. While the preface may give you a general idea of what took place in the previous story, it won’t cover every detail. And why read part two of something without reading part one? If you read Fortune’s Wing: Second Flight before reading the original Fortune’s Wing, it would be more difficult for you to follow the events in the story.
Companion stories are generally for entertainment. You should be able to enjoy them, whether you’ve read the established story or not. For example, even if you’ve never read the Valentine series, you can still enjoy Allan and Mac, without getting confused, and vice-versa. In my opinion, a companion story should be able to stand on its own. Even if you haven’t read Our Lady of Righteous Rage, you can read its companion book, Novocaine.