I think one of the most important aspects of creating a character is giving them goals. Every human being on this planet has goals. We have short-term goals and long-term goals. Even your antagonist should have a clear goal. In this post I will talk a bit about setting goals for characters using my own book, Vampires Rule, as an example.
Short-term Goals: This can be something the character wants to accomplish that day, that week, that month. In every scene I write I like to know what my protagonist is hoping to accomplish; although, I don't always let the reader know. Still it helps to have the information for yourself.
In Vampires Rule, Jack's short-term goals change as we move through the book. There were times when he wanted to make peace with his brother and times when he wanted to save a life. Knowing where your character is coming from, where their mind is at in each scene really helps. It works for me, anyway.
Long-term Goals: These are the most important. What does your main character want more than anything else in the world?
For Jack, the answer is to be normal. He wants to live a normal life, catch up on everything he missed while he was living as a vampire.
Now, what does the antagonist want, and how do his goals clash with what the protagonist is reaching for?
In Vampires Rule, Jack wants to be normal while my antagonist is hoping to turn everyone into werewolves and rule the world. It would be kind of hard for Jack to live a normal life if the villain gets his way. So in the case of Vampires Rule, Jack has to go up against the antagonist. He's the only person who can stop the bad guy, so Jack has to put aside his wants and needs for a while.
When you give your characters goals, remember to think about the other characters in their lives. How do their desires clash with those around them? Also, remember that a character's goals can change. Perhaps they grow up, learn an important lesson and decide to focus on something else. Or maybe they try hard to reach their goal and fail. What happens to them? Will they keep trying like Scarlett O'hara or sink into a deep depression?