Most RPGs are collaborative experiences, the GM and players work together to build a story. Certain things make that easier or harder and they should be carefully considered when building a setting.
- The world should be immersive and detailed enough that the players can quickly understand it.
- Overly detailed and complicated worlds can take people out of the game as they struggle to recall details or figure out how new situations and knowledge fit in.
- NPC's should be diverse and include a mix of ones the players regularly interact with and those that are just background. In very few cases does the GM need an actual stat sheet, even for those frequently interacted with. However the GM should keep notes to maintain consistency and allow the NPCs to grow organically over time.
- The GM should not get stuck on prior decisions. Often the players will inspire new ideas or takes on things and if these things are incorporated the players are likely to feel more invested. This does not have to be obvious or even known to the players. Keep some mystery, let them wonder if this was the original plan or if it changed! That said I sometimes let players know they changed things but only if it wont disrupt the immersion or feeling.
- The GM and the players should be on the same page as much as possible and working towards a mutually satisfying story arc. Strongly guided campaigns (Railroading) are often less work for the GM but unsatisfying to the players who if they feel have no agency will be less invested. Open stories (Sandbox) leave it up to the players to choose and in my experience are a lot like a business run by committee. The ideal option is something in the middle, my preference is more sandbox than railroad but it takes more work on my part and requires me to leave lots of things the players can pick up on and some improvisation on my part.
- GMs that can better predict the players will typically run more interesting (to the players) campaigns and can save themselves a lot of work. Do not be afraid to recycle ideas. NPCs can often be reused with minor tweeks and the same with many plots.
- Related to the above is anticipating spoken and unspoken desires and goals of the players. If a player is interested in combat then combat should be available. If the player is interested in figuring out mysteries, exploration, advancing the world, or just making a difference these should all be considered and opportunities for them provided. Of course different players may have different priorities so time management is important.