Real Life. A concept that didn't fully exist until marriage, kids, house repairs, bills, and the inevitable Real Job (which either one gets because of the situations pertaining to Real Life, or the Real Job forces one into Real Life. It's really a chicken or the egg type of thing).
No matter. All one needs to know is that the beast known as Real Life can really take a chunk out of one's hobbies. I don't care if it's painting, sports, spelunking, or RPGs - Real Life will unapologetically take its unfair share.
So as a time challenged RPGer, I need to get the most bang for my gaming sessions, and that usually means one solid action-filled adventure that can be completed within one night. If we kill the momentum in the middle of a dungeon, having to pick up the pieces again one or two months later...well, that stinks. I hate that. If we had a weekly or bi-weekly gaming session, I could live with an adventure that last three or four sessions.
However, my sessions are too sporadic for such a luxury. Ain't gonna happen.
In order to prepare a one-shot dungeon, I have to understand the parameters of what can and cannot be accomplished in a single gaming session (four to eight hours in length).
1. The quintessential beginning town adventure.
In my youth, I loved starting off an adventure in a town. The inn. Ale. Rumors. Thievery. The supply shop to buy torches (and the "Magic Shop" required in every Monty Haul campaign). The town setting is a great place to Role Play before heading off to the meat of the adventure.
Not in the one-shot dungeon. The town can quickly become a time-eater. Players will get so wrapped up in local affairs, politics, thieves' guilds, and prostitutes, that they will never get to the desired destination: the last room of your dungeon.
Unfortunately, unless the adventure actually takes place in a town, you will need to either strip the city way down or scrap it all together. My modules usually begin in a generic, undefined town, mercilessly devoid of hard details as a simple jump start into the goodies: the first room of my dungeon.
2. Wandering monsters.
Also known as wondering time-eaters. Do you want to burn up enough time so the characters will never find the Lost Artifact of Whatever? Toss in teams of wandering monsters. Even one wandering monster will set your adventure off by one or two "numbered" areas within the dungeon. You will kick yourself when you have to stop the adventure a mere one room away from completion because the party had to take care of a batch of stupid giant centipedes.
To be fair, I do put wandering monster tables in my modules, but I do this for a couple of reasons. 1. Tradition. Can't help it. I rarely use it, but I can't help it. 2. There are folks out there who game frequently, like every Monday, Wednesday, and Friday, and can afford to eat up some time.
3. A map with tons of areas.
Thankfully, I hate creating maps. Hate it. So, for me, the smaller the map I have to create, the better. A small map with some carefully placed encounters will help to ensure a quick adventure. Also, keep in mind that if you really want to write a one-shot adventure, stay the hell away from labyrinths. Holy crap. I learned my lesson when I test-played the Labyrinth Tomb of the Minotaur Lord (available now in Knockspell #3). It ended up lasting two full sessions and the players actually missed a few numbered areas. Boo.
Plus, watching a player try to carefully map out the twisting passages of a labyrinth is the ultimate exercise in tedious time-wasting. Avoid!
4. The use of intricate puzzles.
Puzzles are great fun. The can add flavor and challenge when well-placed in a dungeon. They can also make players sit around for precious minutes, scratching their chins, while wandering aloud what they should do to solve your ingenious time-eater.
This one is always tough for me because I love to place puzzles throughout my dungeons, so the trick for me is to make the puzzle a bit obvious, but in a way that keeps the characters moving. I don't know how to explain this except that the players will know how to solve the puzzle, and the answer to the puzzle can be found somewhere further into the dungeon, so they must keep moving to other areas until they eventually stumble upon it.
This keeps the adventure moving though other important areas. They make progress until they find the key to the puzzle, and then they can backtrack (which is not too wasteful considering I eighty-sixed the wondering monsters).
5. Fast ending.
While I have no problem saying, "Good job! This one's done!" after the characters took care of the dungeon's final encounter, some players need a bit more closure to the adventure. To accomplish a quick ending, establish what will happen at the beginning of the adventure as to what events will follow after conquering the Temple of Fill-In-The-Blank.
Something along the line of a set reward to be given to the characters after bringing back proof to the citizens of whatever evil that plagued the temple is now destroyed. That way, after the characters sweep through the dungeon, you can have them "instantly" return to town (again, since the trip will be devoid of any wandering encounters), do a quick role-play session with the town officials, and close the book on that adventure.
These are just a few pointers I use. One-shot adventures for the busy adult can be fun (or it can suck, but we busy fellers sometimes have to take what we can get), at least to be able to game, even if it is once every other month.