If its long just do as many words as you can post in a single post, and just string them together. There are stories here that have been running for years.
Far as rules, no underage and...that's about all I've really seen as hard and set. Incest has been done, transgender, elf/dwarf, everything but beastiality I've seen (Don't want to either. I'm sure its there, I'm not looking for it.)