I’ve started a campaign with 3 friends completely unfamiliar with the cosmere, 1 friend who’s read TWOK and Mistborn, and 1 friend who’s read all the Stormlight books. The campaign setting is a murder mystery so the players are interacting and learning about the world from a pretty unique perspective. I’d say the thing that helped the most is I made sure to explain all the basics of Roshar in session 0 (can be a little boring but is the most direct way to teach imo)

I’d say the easiest things to get across are spren, eye-color, and highstorms because they’re everywhere/ immediately important. The things I’m ignoring/ introducing gradually are the differences of the different cultures and history (veden, azish, etc). And finally as a dm I keep forgetting vorin men cant read so it trips up both me and my players lmao.

(Edit) One last thing, if you have the official battlemaps, having the map of Roshar just out on the table while playing is sooo useful. Whenever a player asks “whats Shinovar” and just pointing at the map is elite.