So far, I've been making notes and NPCs for the game and plotting out the history of the land. I've been reading: The Player's Handbook, Volo's Guide to Monsters, Xanathar's Guide to Everything, The Dungeon Master's Guide, Guide to Ravncia, Eberron: Rising From The Last War, Mordenkainen's Tome of Foes, The Monster Manual, and some online sources for other things. it's a lot of things to consider and I'm still thinking of how everything is going to connect to each other and what the overall quest is going to be. But as of now, I've been building and thinking of the world and studying the monsters lore and abilities.