>>723406293 (OP)
Make sure to connect multiple different rooms to every room so that your players get to choose how they explore your dungeon. You don’t want basic-ass, linear Skyrim-style dungeons.
Put some kind of landmark in every room to help players get their bearings.
Dungeons should be dark and full of scary shit. Use sights, sounds and smells to render the scene so that it actually feels like a dungeon.
Have monsters patrol around the dungeon. If your dungeon is big enough, put multiple factions of them in there, and consider how members of said factions get along with each other.
Don’t let your players get away with standing still for too long or drawing undue attention to themselves. They’re not visiting a museum, they’re breaking and entering. Set traps and obstacles before them that not only harm them but draw enemies to them if they fail to avoid or disarm them.
If you want to put puzzles in your dungeon, give your players more hints than you think you need to. Don’t give them to them all at once, but give them plenty of opportunities to pick up on clues or find things like keys.