Basic Adventure Design

The following is an outline of a "Gibbsian adventure," the elements that I consider important in any adventure that I make. As usual because Internet, here's the disclaimer: Your Mileage May Vary. This works for me; I offer no assurances it'll work for you.

Please let me know if there's anything I should add in, take out, or otherwise edit. If you have any other questions, comments, or critiques, don't be shy!

A complete adventure needs the following to be successful:

1. PLOT: The plot is an event that happens in the game world that the players’ characters try to prevent, decipher, or solve. It’s important to note that a plot does not have to come externally, as an NPC hiring PCs to do something. A plot can instead be internal, meaning they happen of the PCs’ own volition. Examples include:
1. Finding a missing person, object, or information
2. Preventing something from happening
3. Traveling to a designated area
4. Surviving for a set period of time
2. ANTAGONIST: The antagonist is any person or force that is in direct opposition to the protagonist (the PCs’) goals. An antagonist can be a single living entity, an army or group of entities, or a non-living force (e.g. a forest fire). Antagonists tend to have the following traits:
1. They are defeatable by the PCs, even if it requires a third party element (e.g. a special weapon or piece of information the PCs need before engaging the antagonist) and even if it’s only temporary
2. They have an agenda of their own that they will carry out if not impeded by the PCs. This is possible even for inanimate objects (a fire’s agenda is to consume everything it can before it dies)
3. A history leading up to the antagonist’s involvement in the adventure. This history need not be known to the PCs.
3. SETTING: The backdrop on which the action of an adventure plays out. A setting can be a single area, or it can be a range of areas, and often have the following:
1. Objects or NPCs that can be interacted with;
2. Direct connections to other scenes/settings;
3. A definite sense of place and narrative
4. ACTION: A good adventure tends to have certain, definable action inherent to the resolution of the adventure’s plot. Common actions in an adventure include combat, exploration, social interaction, puzzle solving, information gathering, etc. Important things to remember about action are:
1. They serve towards resolution of the adventure’s plot;
2. They have variables, and can accommodate different ideas/approaches;
3. They have definite goals in and of themselves (e.g. a certain amount of enemies to beat in combat, or a particular pattern that needs to be found from available data)
5. PROTAGONISTS: The PCs are the protagonists. Players make them, run them, and the GM works with them in the resolution of the adventure’s plot. Protagonists who make for good adventures have the following traits:
1. A strong motivation to resolve the plot of the adventure;
2. A defined personality and background that shapes and informs the actions the protagonist takes;
3. A connection to every other protagonist, and the ability to work with them as a team to resolve the plot of the adventure.

The Adventure "No-Fly" List

Although they have similarities, an adventure for a role-playing game is fundamentally very different from the plot of a novel, movie, TV show, or videogame. As of such, there are particular trends and tropes that may work well with those other mediums, but not so much for an RPG adventure. 

A typical RPG adventure should NOT have the following:

1. A solitary protagonist (unless, of course, you're writing an adventure specifically with only a single player in mind);
2. A set course of action that cannot change on a moment’s notice;
3. Essential information or events that happen "off-camera," without the protagonists’ discovery or involvement;
4. A theme that occurs without the players’ involvement;
5. A single ending that happens regardless of the events leading up to it.

Specific tropes that should be avoided include:

1. The "captured" trope, where the protagonists are hopelessly overwhelmed and must surrender;
2. The "invulnerable bad guy" trope, where the antagonist is encountered early in the adventure and cannot be reasonably defeated by the protagonists.

Note that some adventures can have some of these elements in them; however, most don’t. A GM is better off excluding these things for the sake of a good adventure, rather than including them.

This pic has little to do with anything I'm about, but it's kind of cool and came up in a Google image search for "Adventure Design," so what the hell?