You don't have time for fancy theory. You don't have the time to roll on a bunch of tables and plot out each room meticulously. Your session is tomorrow, and you've printed out some Dyson dungeon, with a sheet of coffee-stained notebook paper and a half-empty blue ballpoint as your weapons. You have to make something up, and fast. How will you do it?
NAME. Conquer the blank page. Scribble a name out. First thing you can think of. "Grotto of the Goblin King". There.
THEME. Look at the map, look at your name, come up with a sentence to describe the dungeon, then a single word (two if you really need it) to encapsulate the theme. "A mutated goblin has infested an underwater cave network, using its watery passages to dredge up old pirate's loot. Eroded."
KEY. Number your rooms, then write the number on your page. Leave exactly two lines of space for each room, or a single sheet of your paper of choice, whichever is less. Limit yourself. You won't be making expansive plots or complex puzzles.
CHECK YOUR MAP. See any rooms that immediately afford ideas? Write them down. Get a feel for areas that pop out to you. Visualize walking through the space, and when you have an abundance of ideas, move to the next step.
KEYING ROOMS. Keep things short. Describe things only in terms of what will spark your memory. You don't need a full description, just a few words. "Halfling corpse, goblin conveyor, 3 gobbos w/ slings, dirty syringe" could be all you need for an epic tactical encounter. Keep your theme in mind. If you don't have an idea, look at the theme and the rooms you've filled in. Not every room has to be amazing, many things you can breathe life into at the game table.
TTT. If you get lost, or falter, each room should have a Timer (what happens if the PCs wait too long?), Threat (what opposes the PCs?), and Treat (what can the PCs use to their advantage, or take with them?).
DOODLE. Draw the major features of each room on the map, even if you can't draw for crap. It'll get it to stick in your memory, force you to visualize each room so you'll better describe it, and generally work your brain in new ways. If you get a new idea when drawing, stick with it and run with it.
STATS. Choose the 3 most important monsters in the dungeon and stat them out or find an appropriate stat block. The rest, you can pull from memory or books you have on hand, or improvise. Likewise for traps, magic items, new spells, whatever. If there are more than 3, you can improvise the excess.
PENCILS DOWN. Once you've got most every room fleshed out, put your pencil down. Look back, at your doodles, at your two-line descriptions. How did it go? Does the dungeon feel complete to you? Is anything fun, or necessary, missing? Is there enough treasure? Enough traps? Read it all through and tweak what needs to be tweaked.
SPILLING OUT. "Hey, wouldn't it be cool if the Grotto were in a ship, and the PCs entering would push it off into the ocean?" Write down the excess ideas, the overarching mechanics, the random encounters, in the margins of your notes, or the map. Have them as a fallback, as an inspiration. Right as much as you can right on the spot, and no more. You can fill the gaps in later, chase your creativity.
YOU'RE DONE. With a ballpoint 3/4 empty and a sheet of notebook paper covered in notes about goblin doubloons and dead pirates, you're ready for that game tomorrow.
Check out this post, it's also quite good, if not more panic-motivated. Hope this gives you the motivation to write that adventure you've been putting off, and gives you a couple new tools.