Two lessons I took from a book on writing stick with me still.
1. People look for characters to judge. It goes beyond rooting for heroes and booing villains. Each also needs broader dimensions than fulfilling their part in the plot. Additionally, all the characters in between need enough substance to justify their presence, and like accessories to a sharp outfit, or pretty pillows on your bed, they punch up the whole effect a notch or two.
For heroes, I favor a balance between flaws I can identify with and virtues I wish I had the courage to uphold in the face of adversity.
For my villains I include qualities that help readers pity their twisted nature or faulty grasp of reality. However if you’re looking for a high creep-factor, like zombies, serial killers, and the like; these situations require irredeemable fiends.
2. Characters should get what they deserve.
Throw a party for a serial killer who’s slick lawyer beat the system, and see who shows up; nobody. He doesn’t deserve it. In an airport, an unruly kid gets his butt spanked, and you’ll see a wave of satisfaction across the faces of every old school parent around.
When the knight in shining armor risks life and limb for the damsel in distress, he doesn’t lose her to the court jester in the final scene. When villains torture and take advantage of their hostage, no one’s walking out of the theater happy unless he meets a grizzly end. Anti-heroes don’t get the girl, underdogs do.
So after building tension on top of tension, sooner or later each slight or achievement should pay off with just desserts all around. That’s one element of story telling I truly believe people rely on, like gravity, inertia, and the power of receipts to allow bad birthday gifts to turn into good ones.