Characters are often the first thing a reader falls in love with. Building a detailed and dynamic character can be difficult. Thankfully, there’s plenty of ways to practice.
As an exercise: Pick someone you know in real-life. Describe them as the main character in a story. Think about how they act, walk, talk and any habits or quirks they have. You can also try writing them as a villain for an added challenge.
Then: Insert them into a short story. Try rewriting a fairy tale to feature them or even putting them in the place of a character in a show or book you enjoyed. How does the story change to accommodate them? How do they solve some of the conflicts of the story?