That’s good enough advice and it is something that most writers hear early in their careers. The problem with it is that we also have to make our writing interesting. This means that we have to create problems for our charcters.
That’s how your story starts – with a character who has a problem. The first thing you have to figure out is what this problem is and what gets your character started in trying to solve it. Sometimes this is called the inciting incident. Clara has always been remarkably shy but when she sees Becka picking on the new boy, she can’t keep quiet because somehow he reminds her of her little brother.
But you can’t have your story end here. That would be more of an incident than a story. You have to throw in an obstacle. Clara sticks up for the new boy but she really wants him to stick up for himself. Unfortunately, he’s perfectly willing to let her do it again and again and again.
It works best when you can match your external struggle — Clara vs Becca — with your internal struggle — a shy person who has to step forward to help someone else out. The trick is in solving both struggles at about the same time. How can I do that in this situation? It depends on how I want to set it up. Clara could retreat from helping the new boy — she’s simply too shy and standing up for him actually makes her ill. Or the struggle could be in standing up to him as well — to truly come out of her shell, Clara has to learn to stand up to both friends and bullies.
Setting up your characters isn’t easy but it sure can be fun. Fun? Certainly! All that stuff you didn’t quite have the nerve to pull on your younger brother? Now you have characters to torment!