Hi everyone. I’m going to blab here for a bit, and anyone who is interested in creative writing 
(whether it be fanfiction or fiction) can read on if they’re interested.
Not only are Joint Stories fun, they are an oppertunity to greatly improve your skills and broaden your writing horizons. As you write, not only do you get experience but you learn from the people you write with. You consider new ideas and inspirations for motivating your story-telling. This is how I write/have written joint stories with one or more authors in the past:
Genre: After finding another writer we agree on what we want to write in the general sense. Horror? Action? Fantasy? Maybe a mix? Fantasy-Action? Fantasy-Romance? Or perhaps more specifics. Writing about a zombie apocalypse or space adventures.
Perspective: It is good to discuss how the story will be written. First person (I, me) or third person (John, he). Since two or more people will be writing the joint story, the different parts shouldn’t differ from character perspective because it disrupts the flow of the parts as a whole story. I feel that cohesion is important in this respect.
It is good to establish the two considerations above early on. When beginning a joint story it is best not to plan more than the very basics. The beginning stage of writing should allow for plenty of creative freedom as the writers need to get their footing, so to speak.
Main Characters: While it is possible for the writers to share the same protagonist, I have never written a joint story that way. Sharing the protagonist inhibits creative freedom, as you would always have to deal with the consequences of where the previous writer left-off, or risk the story coming out as less cohesive. It is better for the writers to have their own characters. Two main characters (or multiple perspectives) so long as it’s not a shared protagonist.
Character Relations: It’s not impossible for one writer’s MC to be a school-kid and another a middle-aged amputee, but is is often convenient to allow the main characters to interact as easily as possible. The school-kid and adult could both contribute to the plot of a story, but if they’re not related there is a gap between how they can interact with each other. There should be an affiliation between the main characters, a basis for them to know and interact with each other, apart from the convenience of the plot.
Setting: Small town or city? Desert, rain forest, mountains or snow? Era? Season? Country? Some of the basics that may need to be considered. As I’ve said, this will expand in detail naturally as the story progresses. Before writing starts this should stay as basic outlines.
And now that these points have been established, we can start writing!
Chapters: Joint stories work best written chapter-by-chapter. So the writers take turns writing a chapter. It’s not a big deal if chapter lengths vary (nothing is a big deal when you keep in mind this is meant to be fun). To start off a new joint story I will typically write 1,000 words, which isn’t very long. The writers decide who goes first and that person produces a chapter. Writer 1 writes from the perspective of their main character. They come up with an initial idea of this character, whether it is some key words or a detailed backstory. Then they allow their creativity to flow and write until they finish the chapter.
Upload: Putting stories online is kind of the point. Otherwise the only people who ever read it will be the authors. Uploading a story means it can get reviews and followers. After a chapter is completed it is not immediately uploaded. The other writer(s) read it and give their approval. Approval is only related to two things: usage of the other writer’s characters and whether a happenstance effects the story as a whole. Otherwise you can’t inhibit the creativity of your fellow writer.
Character Profiles: Are a useful way to describe your own characters to yourself, and to the other writer. You can keep details and plans secret, but you should give enough information to the other writer so that they can include your character in their chapters should they wish to. As this is a joint story, both writers’ characters should play roles in each other’s chapters, obviously not every chapter, but enough so that the writers aren’t writing completely separate stories that don’t overlap.
So you have got used to writing, uploading and exploring (and thus creating) the world.
Making the Plot: After say 10 chapters, in which you’ve had a good introduction arc and a goodly amount of exploring, you writers may become interested in creating a plot skeleton for your story. Both writers agree on milestones beforehand, e.g. when the climax will be, maybe you will prepare for a fight scene at chapter 30 that will be devastating and change the course of the story. One writer may compose a plan, send it to the other writer for discussion/modification and then approval. It is a plot skeleton because you fill out the muscle (the details) in typical freeform as you follow the agreed directions of where the story’s going.
NOTE: It is good to plan an ending. Stories are good but completed stories are precious. You and your fellow writer can always write a different story after, or even a sequel, but it is good to plan an ending so that instead of your work being abandoned one day, you can have a nice finished work somewhere that can be appreciated in totality by someone else, witnessing the skills you’ve developed and the way you’ve built your world.
Secrets: One of the great and exciting things about a joint story is that most of it is creative freedom. In this setting you get to improve your skills by making your own plans and adapting to the story as it develops. The other writer doesn’t need to know what you plan to do with your own characters. It’s exciting for both writers to guess what the other one’s planning and what will happen next. So long as what you’re planning is approvable and isn’t so modifying to the whole story to be disputed.
Lastly, a point on
Commitment: Motivation comes and goes. Real world commitments can come in. To ensure that a joint story remains fun I came up with rules for updates/nagging. The Nagging System is effective. To keep the joint story fun and not a chore, each writer has one week to complete their chapter. Within that time the other writer can’t ask about its progress, they can’t “nag” otherwise the week restarts. After one week the other writer(s) has a right to award one nag. After which, they can’t do it again for another week. If the writer whose turn it is knows they can’t get the chapter done in a week or month, all they need to do is say so. They could even pause indefinitely, just let the other writer know of their situation and when they are ready to start writing again, say so.
It is important to note that everything is negotiable. This is simply the way that I’ve found works best for me and the people I’ve written with. Writing with people who have spiritual views, especially occult LHP views can lead to intriguing and deep stories. If anyone is interested in joint story writing you can comment or PM me. Or if you enjoy creative writing or regular writing, we can discuss it and look at each other’s stuff. Thanks.