In the book No Plot? No Problem? author Chris Baty discusses creating two “Magna Cartas” before tackling a fiction project. One is a list of things you like about the genre, what makes you want to read it (or, in the case of a roleplaying game, play it or run it), the things you’ll want to include. The object is to keep you focused on the things that will make it fun to work on. The other Magna Carta is for things you dislike and want to avoid. You make this list to remind you where you don’t want to go, cliches to resist and paths of least resistance to avoid traveling. It’s a process I apply to worldbuilding and campaign building, and a topic I cover at length in the forthcoming Worldbuilding 101 book.Here's my list of likes and dislikes in a role playing campaign setting.
Capricious gods, spirits and suchlike
Characters who relax the way people relax in the real world (sex, alchohol, drugs)
A cold-hearted universe
Mutations of some variety, and/or fear of mutation
Good old British fantasy malaise/fatalism
Dwarves having disproportionate influence
Elves and their imitators
Anachronistic real-world modern-day politics/beliefs
Characters who kick ass all the time or who are overly awesome
Magic item economies
Gods who dispense quests
Giving new names to traditional fantasy races to try to appear innovative. If it's an orc, call it an orc, for God's sake!