Sherylyn and I write as a team.
Back when we signed with our agent we also had to sign a collaboration agreement.
There are a number of standard collaboration agreement samples on the internet, and most major writing organisations have an agreement you can view or purchase. These standard agreements are mostly for a single book. Because we write as a single entity, we wanted an agreement that would cover multiple works, so we wrote our own.
The basics were easy. Decide how much each collaborator gets, who owns the copyright, who signs any papers, how you split the expenses, how your name appears on the book and so on.
It’s catering for the things you don’t expect to happen that cause more trouble.
As Lloyd Jassin says in an article on Absolute Write
Although collaborators might not feel comfortable discussing long-term financial issues or the eventuality of a dispute, or even the death of a co-author, it is always easier and less expensive to deal with these issues up front, rather than later, after a dispute arises.
Absolute Write — Collaboration Agreements in the Publishing Industry by Lloyd J. Jassin
The time to address the major issues confronting contributors and collaborators is before the actual creative process begins.
It was —’fun’ isn’t the right word, ‘interesting’ may be more appropriate—to consider what might happen to our writing in these cases.
There are the standard death and disability clauses. What if one author gets hit by a bus? Does the other author have to finish the book? What do we do about future novels in that case?
There are the other, more unpleasant scenarios to consider as well. What if we split acrimoniously? What if one of us gets a greedy life partner who wants that particular author to keep writing even after the other partner doesn’t, and so on. (Of course, these aren’t more unpleasant than being hit by a bus, but it’s a nasty end to what is currently a good writing partnership.) What if, after the bus incident, the dead person’s life partner wants to okay a d-grade porn movie based on a novel that has already been published?
They’re not questions you can ask when your relationship is already starting to crumble, and they’re definitely not questions that should be answered first-time by the collaborators’ lawyers in court.
If you can’t ask—and answer—questions like this before you start writing together, then you need to seriously ask yourselves whether you are ready to collaborate.