First, some serious tips:
- Have a schedule. Stick to it for three or four weeks straight. After that time, keep sticking to it, but it will be much easier now that you've formed the habit. You don't have to do a lot on any given night that you've committed yourself to, but you have to do something - even if it's just doodling or scratching down some ideas you had during the day.
- Find a different section of the project. Want to map that second floor but just can't find the juice? Work out monster placement elsewhere, or webs of relationships, or treasure troves. (Random Generation can help.)
- If your world is meant to be more than just a single dungeon, work on another part of it. Maybe you're incapable of statting up the Temple of the Umber Ophidian, but you could make some headway on that Shrine to the Malevolent Malvolio you'd been meaning to save for later. Just because the players won't get to it next session doesn't mean it won't be useful.
- Try coming at your work from a different angle. If what you need is monster placement, stats, or mapping, try thinking about the history and present-day uses of the dungeon. Layering interesting bits onto the backstory can fire the imagination with ways to make those bits relevant through gameplay.
"Oh, sure," you say, "but you're not the first person to tell me this. Heck, you're not even the best, with your anemic little four-point list! Give me something entertaining!" And you know, you're right, so here's another, potentially less helpful but more interesting list:
- Play Dwarf Fortress? Combine your hobbies! Build a grand fortress, then lose it in any of the million ways you can in that game, then go back in adventurer mode or history mode to check it out. Lift it directly and plop it down in your world. (Extra points if you somehow theme the dungeon, e.g. everything is made of bronze, or the dungeon contains mechanisms to rearrange itself.)
- Surf the blogosphere. There's some really cool stuff out there.
- Ask a five-year-old
- Perhaps my favorite: run some piece of fiction or fantasy gaming materials through a Dissociated Press algorithm and look for interesting words.