A reader needs to have a reason to root for your MC or at least against your villain. Tvtropes.org has a great article on character-centered plot building. I’m not going to rehash the entire Dramatica storyform theory here. But I do want you to think about a few concepts:
What is your MC’s goal?
Your MC either needs to start doing something or stop doing something. They might need to change themselves or they might need to change the world.
What is your MC’s motivation?
What caused your MC to realize their goal. Even if they MC doesn’t recognize their goal, there are events or conditions behind their actions. How do they go about pursuing that goal?
Do the other characters in the story support the MC’s goal?
Separate from how they feel about the MC and the villain. Supporting characters have motivations of their own. Do they want the hero to succeed or fail or is there a third option?
Are they opposing or supporting the MC?
This is not the same thing as supporting the goal. Every character described should have an impact on the MC the Villain or both.
By giving thought to these questions, you will find the depth of your stories filling out and you might even see a way to resolve a plotline that has had you stumped.
What are some of the tools that you use to develop your characters? Keep writing my friends!