I don't know if there are any particular guidelines, but I did learn about a year ago that there is a word that describes the practice of coining words.

logodaedaly (10/28/99): The arbitrary or capricious coinage of words.

One of my favorite, personally coined, words is one I use almost daily. When passing coworkers in the hall, one will almost without fail ask "How are you?" (or something along those lines.) I know the question is rhetorical, but I respond anyway. My response is most likely to be "Peacherrific"