|Picture Credit: http://commons.wikimedia.org/wiki/File:Plutchik-wheel.svg|
Have you ever run into a cast of characters who all seem to react identically to every possible scenario?
There are two things you should do to make sure this never happens to you and your characters. First, you should create a character arc for every major and secondary character. Next, you should pick out an emotional pallet for each character.
Your character arc doesn't have to be a complex graph. Just start by taking a look at what the character wants and fears. Remember, each character in a story thinks he or she is the main character. What does the character want to accomplish? What is he or she doing to work toward that goal? What are his or her biggest hindrances? How does his or her past factor into all this? A person's past always influences how they think and what they do. Knowing your characters inside and out will make them work together and clash against each other in believable ways. In every scene you should know what each character present wants to accomplish.
Now you need to come up with your characters' emotions. What is each character's base emotion--on an average day what feelings does he or she have? Is she bored with her life? Is he terrified that his great secret will come out? Does she have a nagging drive to prove herself? Does he feel overburdened? Each character's base emotion will be different. Now look at how different stimuli will affect each one differently. A character who is confident about herself will react differently to bullying than a character who is trying desperately to hide behind fake confidence. It is the same with every character and every stimulus. As you look at your characters' strengths and weaknesses, you should be able to develop a list of emotion words that describe them in different situations.
And don't overuse happy, sad, scared, mad...or any other bland emotions that don't go into much depth. I used a picture of the Plutchik Wheel to introduce this topic, which is a wheel of emotions developed by Robert Plutchik. But this wheel doesn't expand our emotion vocabulary much beyond basic emotion words. W. Gerrod Parrott's Inventory of Emotions will give you many more words. Look at a thesaurus for more ideas if you need to.
By the time you are done with each character, you should have a unique list for each one of your characters. Try not to let the same emotion word describe any two. Then when you are writing you can look back at the emotion list for aids in describing how a character feels and reacts.