The first and potentially most important decision a Dungeon Master in Dungeons & Dragons 5e can make is where to set their campaign. This seemingly simple choice determines every single other aspect of the campaign, and subsequently, every session. There are innumerable pre-made locations to set a campaign in, but for the homebrew DM, it’s an even tougher choice because the only limitation is imagination.
Source:https://www.cbr.com/dnd-5e-homebrew-setting-and-tone-guide/