An RPG GM has many of the same tasks or duties as a game designer. Even though what I’m saying today can be taken as game design advice, it also applies to the GM as he/she creates an adventure, even as they prepare to run an adventure created by someone else. "A hero ventures forth from the world of common day into a region of supernatural wonder. Fabulous forces are there encountered and a decisive victory is won." Joseph Campbell
Film students are often taught that successful films and other stories - or perhaps just tragedies - always have three "acts;" but others suggest maybe five or nine acts, or seven points, or something else. I'm not going that far, but I will say that in games, if the game doesn't have phases where what the player does and thinks about changes from one phase to the next, then it had better be a short game or it's going to get tedious.
There are MMOs (Massively Multi-player Online games) where people do the same not-very-interesting thing over and over again, called “the grind.” In fact it's so simpleminded that you can have bots (small automated programs) do it for you, and it can be so tedious that people are willing to pay somebody else to do it, and then buy the results (with real money). I would rather design a game/adventure where people enjoy the journey as well as the destination, so I try to avoid "the grind."
There are lots of ways to define these three acts, going all the way back to Aristotle 2,500 years ago. The first act includes introduction of characters, and exposition of problems/conflicts. In the second act, the protagonist takes on various obstacles, usually an antagonist is involved, and this can be the darkest act when things look really grim. Then in the third act, you have a resolution or climax where the protagonist overcomes the obstacles, and a denouement - what happens afterward as things get sorted out.
There’s plenty of disagreement about the ideal way to construct stories, which leads us to the modern notion of the Hero's Journey. This was identified by Joseph Campbell in the book The Hero with a Thousand Faces in1949. The original Star Wars movie, apparently deliberately, tends to follow the Hero’s Journey, with a call to adventure, an initial refusal to get involved (until Luke’s family is killed), a mentor (Obi-Wan), and on through many stages.
Entire books other than Campbell's have been written about the story form. If you're into story creation you might read some of those books; but is it necessary for designing games and adventures? No, often the "story" is just an excuse to get to the action. Many adventures are about overcoming obstacles, not about stories, but what players and GMs prefer varies a great deal.
Game designers design games, GMs design adventures, neither have to design stories. But some do. Some game designers (and some GMs) are frustrated novelists; they should become familiar with Campbell’s ideas.
The Hero with a Thousand Faces (1949), Joseph Campbell
The Writers Journey: Mythic Structure for Writers, 3rd Edition (2007), Christopher Vogler
contributed by Lewis Pulsipher