Every character needs a reason for their actions, reactions and desires. Making sure the motivation is a strong one is essential to great story telling. Discovering each character's motivation can be easy or it can be hard. All the major characters need a strong motive for doing and saying what they do. This includes the hero, the heroine and the villain, even if the villain doesn't have a viewpoint section in the story. Some of the secondary characters also need a motivation. Theirs can be strong but more siple than those of the major characters. Usually they are to help or hinder one of the other characters. What about those minor characters, ones who are more like walkons. Their only motivation would be their reason for being in the scene. The waiter or waitress to deliver the meal. Just make sure they follow their reason and don't interfere in the scene unless there's a reason for this. The reason should be one the reader can see.
Things to ask that can give a hint toward motivation. What did he or she mean by that action? Why did he or she say a particular thing?
Remember in real life we can't read another person's mind but we can speculate as to why they act or speak a certain way. The question of motivation will go unanswered. But in fiction, the writer must know the reason for the characters to behave in a certain manner and the reader needs to see the reason.
A character's motivations have two purposes.
1. to define actions
2. to fit the plot
You wouldn't put a canracter bent on destruction of another person in a light-hearted romance. This is the sort of thing you must consider when writing your story.
So we'll be looking a ways to make sure the motivation for your characters is strong. Weak motivations make the readers turn away from the story.