Ben, of the YouTube channel Questing Beast, is a very talented fantasy mapmaker and dungeon designer. In this video, he runs through nine principles he applies to dungeon design.
These principles include everything from the basics, like making sure you have multiple entrances and exits and appropriate level challenges to thinking about what the dungeon originally was (an actual prison? fortress? trap? etc.) and letting that inform its design to creating dungeons that loop, that are networks (not liner, not tree-like) and adding three-dimentionality to your dungeon spaces (multi-story rooms, galleries, gangways). Solid reminders of good dungeon design.