I am going to focus on fantasy, but as a player, I, generally, want many of same things in post-holocaust or space opera (with some variation due to genre):
1. A map with the various nations from which PC can hail? What are the major natural geological features (bodies of water, deserts, forests, mountains, islands, etc.), nation boundaries, towns, cities, etc.
2. The player races available?
4. The culture(s)within the races and where they found. I also want the DM to think about aspects of the culture such as the following (and some things may be based on other decisions)
a. What is the subsistence of the society foragers, pastoralists, horticulturalists, agrarian?
b. What is the technological level?
c. What is the social organization (band, tribal, chieftain or state)?
d. What is the social stratification (e.g. egalitarian, class, caste)? Is the society a democracy, matriarchy, monarchy, oligarchy, mageocracy, theocrachy or something else?
e. What is the belief system (e.g. animism, shamanistic, polytheistic, monothesitic, syncretism)
- In a polytheisitc or monotheistic society: whom are the gods - their domains, symbols, any sacred animal/creatures priesthoods (including a strictures, vestments, some holy days, tailored spell lists)
- in a society where spirit worship exists- animistic or shamanistic (one religious leader)- what the the major spirits?
f. What are the classes, class variants (if any), and subclasses found or not found in the society? The same for backgrounds.
g. Have some cultural guidelines on things like naming conventions, body adornment, views on magic, property ownership, and crime/punishment
i. whom are are the important NPCs (e.g. rulers, powerful wizards, religious leaders) and organizations (e.g. wizard academies, merchant guilds, thieves guilds, temples of deities) (if any) within the society whom my character might now and have ties. General notes are fine.
j. what are some things that my character would know based upon growing up in a specifc culture and even might know based on their class which might provide hooks or goals for my character?
- noteworthy current events (e.g. feuding noble houses, an attack by a wizard's guild on religious leaders, the abduction of someone noteworthy, a usurper to the throne and a rebellion to take the throne back, mysterious lights in a forest, etc.), rumors or gossip.
- past historical events of note (e.g. a war or long animosity with a neighboring people, a deity appearing where a temple dedicate to them is now located),
- or other things such as possible adventuring sites (e.g. a haunted location, trolls in the local swamp)
- a secret society based upon gender, age, social status, and/ or or character class
As a DM, having the above worked out prior to character generation helps me get everyone on the same page and ground pcs in the setting. In play,it also helps me when I need to answer questions or improvise- especially, when players choose to change direction in the middle of a session
What I do not need as a player are migration patterns, names of different coinages, minute details of architecture, etc.