Orson Scott Card's Characters & Viewpoint today. Building tension engrosses the reader & aids them in the course of caring for the characters we invent. There are 5 methods writers employ to do just this.
You wound me, sir - Make them suffer; emotionally &/or physically. The story & characters determine which is appropriate. Whichever the characters are enduring needs to follow the believability predetermined by the author. And, the reader needs to be able to bear the pain alongside the character. However, there is a fine balance between too little & too much. Rhett Butler's departure at the end of Gone With the Wind is the last wound we know Scarlett cannot bear. But, rather than expound on how she fumbles through life, Mitchell leaves the rest to the reader's imagination.
Bring in the lamb - Sacrifice. Either the MC is throwing themselves down the pit or another character. Or, a minor character sacrifices him/herself for the greater good of the hero/heroine or another ideal. All sacrifice is relative to the choices characters make. When Boromir throws himself into the protection of Frodo, the reader is more emotionally involved because of his earlier deception. He is redeemed through his sacrificial choice.
This is Jeopardy! - Anticipated pain, suffering & loss. The level of jeopardy is directly tied to the amount of pain - a double sharp edge that will cut both ways. In Stephen King's The Girl Who Loved Tom Gordon, the reader is carried through the story with a radio that will cut off the MCs connection to the world. As fear mounts, irrational thought creeps in the back door building tension & increasing the level of emotional involvement.
My, aren't you attractive - The building blocks of sexual tension; even when it's not about sex. Not every romance results in the sheet-twist. But, it does provide a story line readers enjoy. A perfect example of how not to go to bed on the page/screen is Shrek & Fiona. It is the anti-attractive romance because ogres ain't pretty. But, viewers find the feeling genuine & invest in the pairing & believe in the attractiveness of the pair. They have kids, but they don't engage in sex. And, that, can be just as escalating as the act itself.
The birds, crows & owls - A sign of things to come. A character's connection to his/her universe creates strong descriptors for that world at rest & embroiled in chaos. My favorite example of this is The Wizard of Oz. Dorothy's race to beat the twister; which does triple duty to re-order her world, her view & her place in it all. Without that single event, Dorothy wouldn't be thrust to change or Oz for that matter. Readers & viewers care because while the story is fish-out-of-bowl, it is also coming-of-age. And, we identify with her plight, her journey & her eventual change through the use of the natural/unnatural world to teach deeper internal lessons tied directly to Dorothy's apron strings. The signs are all around her & the reader.
Tension is built to increase reader involvement & to push characters to their change point. This change point is not unlike the boiling point of water. The seconds just before the roil begins are just as important as the build & spill when the pot gets too hot to handle without mitts.