I am thinking of doing something with one shared prompt for everybody, and a date after which I will start compiling a masterlist. Perhaps I would add optional challenges to the prompt, but the only real requirement is the single shared prompt. I don't think a deadline is useful; if somebody writes to the prompt a year after the date, I'll be happy.
What's the right way to promote without being spammy?
Where's the line between relaxed enough not to be stressful, and structured enough to be motivating?
Pointers to existing advice, helpful anecdotes, and primal screaming are all welcome.