The Four Aspects Of A Roleplay Campaign/Plot
(Or, How To Make Designing RP Campaigns/Plots Easier!)

The four main RPG campaign/plot aspects

Pretty much every game experience can be divided into some combination of the following four aspects: Social, Problem Solving, Discovery, and Combat. Here's an overview of how they work, along with an estimation of how much prep time they need and how much crunch (die rolls and all that) they require:

SOCIAL: Characters meet, get to know each other, discuss world events, argue, play games, make friends, fall in love, and all that fine stuff. This can also include court intrigue, office drama, art contests, etc.
Estimated prep time: Low to moderate. All you really need is a place for the characters to gather, and a reason for them to be there.
Estimated crunch required: None to low. No die rolls are needed to maintain a game where everyone is simply interacting with each other, though dice can add an element of unpredictability to any NPCs they might interact with, and can be useful for determining winners of contests.

PROBLEM SOLVING: The characters (or rather, their players) must use their problem solving skills to advance the story. This could entail escaping a veritable puzzlebox of a castle, infiltrating a secure base, or getting past obstacles along a dangerous road.
Estimated prep time: Moderate to high. It can be hard to make up challenging puzzles on the fly, so you'll probably want to work them out ahead of time.
Estimated crunch required: None to moderate. Problems can be solved purely through the wits of the players, removing any need for dice. For example, opening a door may involve working out the location of a key through a series of clues. Likewise, a mystery campaign can be run this way.

DISCOVERY: Characters poke, prod, and explore the world around them in the name of seeking knowledge and sating curiosity. This could involve characters investigating a strange new world they've been dropped into, visiting alien planets for scientific or sociological research, or checking out a spooky old castle to see what's inside.
Estimated prep time: Low to high. While a healthy amount of preparation is always good, it's also possible to make up quite a bit as you go along.
Estimated crunch required: None to moderate. You can have players roll dice to see how successful their efforts are (say for example, opening a locked door or translating an old scroll), or you can just let things work in a simple, straightforward manner similar to the diceless approach for Problem Solving.

COMBAT: Characters fight each other, whether it's PCs vs. NPCs, or PCs vs. PCs.
Estimated prep time: Moderate to high. You have to determine the stats and attributes of anyone and anything that's going to be involved in a fight.
Estimated crunch required: Moderate to high. Whether simple or elaborate, some kind of system is needed to determine who wins the fight. Otherwise, you often end up with players caught in a deadlock where both are equally determined not to lose to the other.

How to decide which aspects to include or emphasize

Know what your players want. No matter how well-developed or awesome your ideas are, it just won't matter if it's not the kind of experience your players are after. If you aren't sure what your players want, ask them. You can even have them rate each aspect on a scale of whether they hate it or really enjoy it. From there, you can tailor your campaign accordingly.

Ask yourself how much time you have to prepare. If you don't have much time, you probably don't want to aim for high amounts of Problem Solving and Combat. Instead, you might emphasize the Social and Discovery aspects, which can make a pretty decent combination. (See media examples below.)

Ask yourself what you have the ability to run. If you lack a functional combat system, you'll probably want to forgo much in the way of fighting. This could mean minimizing combat and relying more on Problem Solving to challenge your players. Thus, defeating the Big Bad might not be a matter of winning a fight, but rather a matter of finding and exposing the evidence that will get the Big Bad sent to prison.

Remember that variety is the spice of life. Any game that focuses on one aspect alone is likely to get boring before long. Purely social games will stagnate and die once the characters run out of things to talk about, but new dangers and mysteries can give them new conversation material. Problem Solving isn't very fun if it's just a bunch of scientists sitting around running tests in a lab all day, but putting them out in an unexplored environment full of new things to discover, poke at, and possibly get attacked by makes things a lot more exciting. Explorers out on a quest to discover new worlds should usually work together as a team, but characters who haven't socialized enough to bond with each other are less likely to cooperate and stick together. Combat can certainly be exciting, but without some Discovery, Social, or Puzzle Solving motive behind it, what's the point? So remember: while each aspect can make the game interesting in its own way, on their own they can't keep a game going for very long. Make sure your game is multifaceted!

Remember that too much crunch bogs down the story, and that's not good. Rolling dice (or drawing from a hat, or using some other kind of randomizer) can make things more exciting by adding an element of uncertainty, but it does tend to take a little time. A game that requires a die roll for just about everything is going to be a sluggish game indeed, and almost nobody wants that. So try not to make your crunch requirements any higher than you genuinely need, and try to avoid structuring a game that's going to end up being all dice all the time.

Examples of the four aspects in media

Not sure how these aspects might look in practice? Not sure what kind of story you should model your own campaign or plot after? Here are some well-known works of fiction you might look at for ideas:

Alice's Adventures In Wonderland: (book) This story about a child finding herself in a strange and bewildering world features a strong Social element, a little Problem Solving, and some Discovery.

The Avengers (2012 film): A story about a team of superheroes who must stop an alien from taking over the world. It features a lot of Combat and Social, with some Problem Solving along the way.

Moana: A story that focuses on a young woman and a demigod out on a quest to save the young woman's island, Moana features Discovery, Social, and Problem Solving.

Saving Private Ryan: As a war film, Combat features heavily. In addition, the story features elements of Social and Problem Solving.

Star Trek: The Original Series: Focusing on the adventures of a starship crew in search of new life and new civilizations, Star Trek is heavy on Discovery and Social aspects, with a big scoop of Problem Solving and a sprinkling of Combat.

Star Trek: Deep Space 9: Heavier in Social elements than other Star Treks, and places a bit more emphasis on Problem Solving than Discovery. Combat increases as the series gets into the Dominion War.

The Wizard of Oz (book): This story features quite a bit of Problem Solving as Dorothy and her friends navigate the strange and often dangerous land of Oz. It also features a little Social throughout, and toward the end has some Combat.