How does a reader get an expectation of reaction? Motivation. As writers we put characters in situations and give them motivation. Even villains must be motivated to act badly. The hero/heroine/protagonist must react in a manner consistent with their motivation. The reader will fling a book faster than you can say, "...but she acted that way because of something I haven't told you yet." A reader creates your story in their mind based on the character's motivations, goals and conflicts. The ones you put on the page--not the ones that you have in your head. Having a character react out of, well, character, is like listening to someone sing off-key. It is a sure sign that the writer needs to work on their craft.
How can you prevent your writing from sounding off-key? Get out of your head and into your character's. Imagine you are your hero-with all his goals, motivations and conflicts- and you walk into a situation just like the one you are writing. What would you do? How would you react?
As a writer I love this part. I have time to think of snappy come backs or cool actions. In real life there is no do-over. In real life, I usually think of something I should have said or done hours or even days later. But as a writer I can ensure my characters give the best reactions to good and bad situations. I have the time to think of some action or witty dialog that will make the reader fall in love with my character. Yes, this takes time. There is no personality chart, no horoscope or middle child/oldest child chart. There is only you acting out your character as written-not as you want to be written. Would they really say this? Would they really do this? If they must, then you have to go back and motivate it.
Take the time to play pretend. Get into your character's head and before you know it your actions and reactions will ring true.
What tips do you know that will help create "real" actions and reactions?