There is a direct correlation between how much stress/relief you provide a reader during your story and the emotion they feel about it after it's over. How passionate your reader is about your work will determine how many people they tell about it.
So how do you make them feel those peaks of stress and valleys of relief? Well, the first thing we have to do is make our characters compelling and relatable (Blogger tells me this isn't a word, but Webster says it is... I'm going with the dictionary on this one, sorry B). If our readers don't care about the characters, then why would they care what happens to them?
Another important aspect, is to make sure the conflicts are both central to the story and that they incite a change in the characters. Characters that are evolving = much more intriguing.
We can also make the stakes huge--to the characters. Every story can't be about saving the world, but if our main characters feel like the stakes put their own lives, happiness, future, etc. in jeopardy--it will be just as moving.
Another way to bring emotion out in the reader is to make the scenery itself, match or conflict with the emotions (mostly with really powerful emotional scenes) within the scene. A peaceful emotion within a peaceful scene makes the reader feel one way, but a peaceful emotion within chaos makes them feel something different. Just don't stick a powerful emotion in a lame scene with no power--Go Big or Go Home. ;)
I discovered this last tip way back when with my first book, ORACLE. There are a couple of scenes where Lexi is feeling seriously messed up--utter inner turmoil. In one scene, the world around her is also in chaos. In another, she's curled up in a tire swing in the backyard on a quiet night trying to hold perfectly still so no one will find her.
Which one got a bigger response from my readers? The tire swing, every single time.
Anyway, what do you guys do to pull that perfect response from your readers? As a reader, what aspects of a book make it the most powerful for you?