Look at the bestseller lists of eBooks these days and you'll find a peculiar phenomenon. Short story bundles and boxed sets are reaching unheard-of popularity, with even the likes of Jeffery Deaver and John Sandford joining in. The reason for these multiple sets is not that they make so much money for the writers. In fact, in many cases the royalties are all donated to a favorite charity. The fact is that every collaboration is a great author marketing opportunity for every writer involved with it. You don't have to be a famous author to get in on this marketing genius. It's a viable plan for any writer, regardless of his publishing history. 
Why Do It?
The answer can be summed up in one word: exposure. The words you write for a collaboration are in lieu of payment for a great book marketing campaign. You create a piece of a product that sells well and, in return, your name and links to your sales page end up in front of thousands of readers who might otherwise never find it. If you've only published one book, this might be a small reward, but for writers with large back catalogs this sell-through can be a gold mine in new, loyal readers and fans.
What Products are Selling?
These bundles are mostly made up of groups of short stories within a theme. Locked room mysteries, international romance, love stories about cooking--find your own unusual niche and exploit it. Some smaller numbers of authors are collaborating to each write a chapter in a novel, but the easiest method is to create a collection of connected short stories. The length of each story is up to the members, but the complete book should be the length of the average full-length book in your genre. Romance bundles usually end up at around 50,000 words, while thriller volumes can almost double that amount. The simplest way to increase the volume is to add more writers to the mix.
How to Find Collaborators
If you write in a niche you probably read in it, as well. You know the big names in your genre, as well as those up-and-coming writers who have the talent but need more experience. Check their book listings for email addresses and simply ask for them to join in. Have all the details worked out ahead of time so you don't waste writers' time with a lot of back and forth questions. Plan everything months ahead to allow for writers' schedules with publishing and current work. Get a firm commitment from each agreeable writer on the word count you can look forward to.
The Bottom Line
Allow every writer in the book to create their own page of back matter, promoting their catalog, newsletter, or website. They can decide where they all want the marketing to funnel toward. As for income, the royalty from a book split a dozen ways or more adds up to pennies on most boxed sets. Many groups have decided on a charity and agree to donate all proceeds after giving the leader of the group a nominal fee for administration. For groups who want to keep the cash, there are companies online who specialize in creating these books, sending out tax forms and doling out the money on a regular basis. Save yourself the headaches and pay them their well-deserved small fee before trying to do this job yourself.
Keep the Faith and May the Force be with You!
