I, personally, don't know of any specific guides. Use real life history and other fantasy settings as a guide. Like for the size of settlements, most shouldn't be more than 100-200 people, a big city would have 10,000 to 20,000 people, a truly massive metropolis would have 50,000 to 100,000. Most people would be farmers/serf, the lucky few would be tradesmen, an even luckier fewer still would be merchants, then even luckier the nobles, and finally the royalty. Also adventurers, like the player characters, are exceptional individuals. They may rise or fall in status due to their deeds. Not every farmer has levels in a player class (like fighter, wizard, cleric, or rogue) having levels in a player class means you are a cut above the normal member of society (a level 1 fighter PC is usually far better at fighting than some poor conscripted peasant footman), even the normal nobles. Most societies would be some form of mono-ruler (Monarchy [rule by one for the overall good of the all] or Dictatorship [Rule by one for the loyal few/the one]), or rule by the select few (Aristocracy [rule of the few for the all] or Oligarchy [rule of the few for the few]). Very few areas (if any) would have mass-rule (Polity [rule by the majority for the all] or Democracy [Rule by the majority for the majority]). Magic and divine influence are real in a fantasy world but don't often affect the everyday lives of the majority of the populace. As far as what player characters would know, local laws to where they live, how the weather and surrounding areas are like, etc. think about what you know about your hometown/country (You know your hometown pretty well, you know who the PotUSA is but probably haven't met him).