You come to a point in your story where there's a conflict between characters. How do you describe their actions/feelings? The one thing you don't necessarily want to do is say something like - John was angry. A better way to describe the situation might be something more along the lines of - A muscle twitched along John's clenched jaw. Showing how your character feels is more effective than telling how he/she feels. It allows the reader to connect to the character in a more authentic way.
This holds true in other situations, too. Action moves your story. It allows your reader to see the emotion in the scene. Jane felt like crying. "Don't go," she said. With a couple of changes, you can show Jane is feeling emotional without literally spelling it out. Her lips trembled. "Don't go."
That being said, remember "less is more." All it takes is a couple sentences to get the job done.