Make a Tabletop Role-Playing Game Adventure in Ten Minutes

Here's a quick and easy method to come up with the outline for an adventure. It involves three steps.

1. Your Concept - Whatever the main image or idea you have in your head, the thing you want to base the adventure around.

2. A Plot Hook and Skeleton - Something to draw the players in and a basic plot structure of events and locales for them to follow.

3. Use of PC Elements - Be sure to include at least one small feature that caters directly to each of your player characters' strengths or character background.

How To Do Step 1: Brainstorm a whole bunch of crazy ideas or scenes. Keep them all as a list or a computer file to refer to later.
Example: Giant-Sized Lizardfolk and their pet dinosaurs.

How To Do Step 2: Look around your room or your house. Find the first thing that has its own plot already - a movie, a book, a pre-generated RPG adventure. Write down the basic elements of that plot in order to translate them into a plot of your adventure.
Example: Romeo and Juliet.
The Hook: The players get involved in a street brawl with members of a rival in-game faction (R&J Act 1: Scene 1).
The Plot: 1. The local NPC authority intervenes to stop the fighting and declares that further altercations will result in some severe punishment. (Act: Scene 1)
2. A ball or dance is held at the stronghold of the PC's rivals, which they must crash or infiltrate. (Act 1, Scene 4)
3. During the gathering, the PCs make contact with a woman within the rival faction who secretly allies herself with the PCs. (Act 1, Scene 5 and the famous 'balcony scene'.)

How To Do Step 3: Look at each player's character sheet and make a list of the game mechanic strengths from each. Make a seperate list of notes based on any background the player has for their character, with special attention to any names or people from the PC's past. Now pick one item out of your list for each PC and incorporate those items into your adventure.
Example: There are three PCs - one is a fighter with a high Strength, one is an assassin with a special ability to become invisible in shadows, one is a spellcaster.
Elements: 1) An obstacle that will require high Strength to overcome. 2) An opportunity to become invisible in shadow in order to aid the party. 3). An opportunity to use magic.

Incorporating the Elements: 1) The fighter will be most valuable during the initial altercation. He can also be valuable crashing the ball. Put a courtyard wall or a stout gate in the PC's way so that the fighter can either climb it or break the gate open.
2) To infiltrate the ball, give the assassin conveniently-placed shadows from which he can eliminate some sentries. Alternatively, give the assassin a shadowy spot from which he first views the PC's female ally and overhears a conversation that tips the assassin off to the fact that she secretly wants to aid the PCs.
3) Make the "Juliet" secret female ally a rival spellcaster.

Now, combine all the elements together. Using the examples from above, our new adventure looks something like this:

The Hook: A group of giant-sized lizardfolk and their pet dinosaurs have been terrorizing the PC's local town, a town where lizardfolk form an important part of some larger rival faction within the town government. The hook for the adventure has the PC's encounter some of the lizardfolk on the street, and the lizardfolk exchange insults with the PC's before attacking.

The First Scene - Street Brawl: The PC's fight a group of oversized lizardfolk and possibly a few of their attack dinos as well. After a certain number of rounds, the local constabulary arrive and put the fighting down, then declare that further fighting between the PC's faction and the lizardfolk will result in the death penalty for all those caught.

The Second Scene - Infiltrate the Luao: After the fight, the PC's either find clues on the bodies of the slain or learn from their allies that the leader of the lizardfolk will be attending a private luao at the lizardfolk stronghold. If the PC's can capture or assasinate him, the rewards will be great. They face a set of small obstacles to enter the stronghold: 1) How to disguise their presence. 2) Breaking into the gate or getting past the courtyard wall and avoiding or eliminating the sentires.

The Third Scene - The Chieftain's Daughter: Once inside the luao, the party's assassin encounters the daughter of the lizardfolk cheiftain. There are convenient shadows about, so he hides. Make sure the assasin player doesn't get the opportunity to simply attack or capture her (although that's certainly an option you could plan for) before she drops some clue that: a) she's a spellcaster and b) she's sympathetic to the PC's cause/faction. This gives them a choice - do they still carry out their original mission or do they seize this opportunity to gain an ally on the inside?

That should be enough for a decent game session, and all within 10-15 minutes. The rest is just hammering out the details: Maps of the street, courtyard and ballroom; statistics for the various NPcs, and so on.