Write like your favorite author!
Create a pastiche of your favorite writer! Heck, it doesn't even have to be a favorite writer. The pastiche can be any length, in any format you wish it to be, from poetry to vignette to flash fiction.
Start a new chapter, title it "Write Like... [author name]"
Write in the style of your selected author. This is harder than it seems but is ultimately rewarding, even if the outcome belongs in an outhouse.
I originally considered having the protagonizer choose the author for the next chapter, but I found this would run against the spirit of things. So choose your own author to emulate, and feel free to make suggestions as to who the next protagonizer should undertake. The subsequent contributors do not need to use these suggestions but come up with their own writer.
Also, if you wish, explain why you picked that particular writer to do this pastiche.
I'll get the ball rolling, and hope y'all will join in for the ride.