Increasing what characters stand to lose (or gain) as the story progresses, making each new obstacle feel more consequential.
Raising the stakes means escalating the consequences of success or failure as your story moves forward. Early on, the protagonist might risk embarrassment. Midway through, they might risk losing someone they love. By the climax, they might risk everything - their life, their identity, the fate of people who depend on them. Stakes can be external (physical danger, financial ruin, war) or internal (self-worth, relationships, moral integrity), and the best stories escalate both simultaneously. The principle is simple: the further into the story the reader gets, the more should be on the line.
If your story feels like it plateaus in the middle, the problem is almost always stakes. Readers stay engaged when they feel the situation getting progressively more dangerous, more personal, or more irreversible. Raising the stakes is how you earn your climax - without escalation, the big finale feels like just another scene. It's also how you prevent the dreaded 'sagging middle,' because each new complication should make the previous ones seem manageable by comparison.
Walter White's stakes escalate from 'pay for cancer treatment' to 'protect my family from drug lords' to 'preserve my empire at any cost' - each level making the last look quaint.
Stakes escalate across the trilogy: survive the arena, survive the next arena, lead a revolution. Each book raises both external danger and personal cost.
The stakes are entirely emotional and relational - we gradually learn what Fleabag has already lost, and the fear of losing more becomes almost unbearable.
Bigger explosions alone don't create investment. Make sure the emotional and personal stakes escalate alongside the physical danger.
Start lower than you think you should. If you threaten the end of the world in chapter two, chapter ten has no room to escalate.
Generic danger is less scary than specific danger. 'She might die' is less gripping than 'She might die without ever telling her daughter the truth.'
Write a sequence of three connected scenes (a paragraph each) where the same character faces the same type of problem - say, lying to someone - but the stakes escalate each time. Scene one: a white lie to a stranger. Scene two: a significant lie to a friend. Scene three: a devastating lie to someone they love. Notice how the escalation changes the character's emotional state and the reader's investment.