Aristotle was an early advocate of plot. He held that a play should have three acts: a beginning, a middle and an end. The modern screenwriting guru Syd Field advocates a similar outline, with the end of the first and second acts punctuated by a plot point, a turning point key to the screenplay. Gustav Freytag, a German playwright, summarized this plot as a beginning, where a conflict is revealed, complications to the situation, a climax in the middle, falling action where the conflict and complications are resolved, and an ending, where the stresses of the conflict become relaxed.
Plot devices are a type of literary technique that advance the story or plot. Again, Aristotle is a good place to start. He described several types of plot devices, including the Reversal---when a situation suddenly becomes the opposite of what it appeared---and the Recognition---when shocking information is revealed. Orson Scott Card, an advocate of character-driven drama, favors the Macguffin, an object, person or idea that motivates characters the viewer cares about to act.
Another way of creating a story is to start from the characters and build a story around them. Even notoriously plot-structuring author Syd Field calls characters "The heart, soul and nervous system of your screenplay." Consider creating a character from scratch and building conflict based on his nature. For example, in the novel "Contact," by Carl Sagan, the protagonist's life revolves around a love of science her father inspired in her, as well as a rebellious streak. As a result, this character has many conflicts built into her personality.
Conflict is the driving force in all drama. There is simply no story without one force going against another. Conflict can be categorized by what the protagonist (the main character) is up against. Common conflicts include man vs. self (internal conflict), man vs. man and man vs. society. Often, a conflict can happen on several different levels. A solid conflict is the foundation of a solid story.