Ok this one is pretty simple:
Simply use a new word starting with the double letter of the word previously posted.
So for example one may post the word BANNED
So the next one who posts must type a word starting with the letter 'N' (b/c the previous word, BANNED, had double letter N contained in it) and the new word must have a double letter in it.
2nd person posts something like NABBED
3rd person posts something like BETTER
4th person posts something like TRIPPED
as so on it goes...
I will start off...