A reader has to engage with your characters to care about them or they won’t finish your story. You, as the writer, must figure out the details. What do you know about your character? What brings them joy? What scares them? What are their values? Do they have goals?
As you write your story, think about your character. Whose story is it? What do they want? What stops them from getting it? How do they get it? Put your character in a new situation. Is his everyday life disrupted?
Think about voice. You don’t want all your characters sounding alike. If you took away the dialogue tags, can your reader distinguish each character without them? Does your character repeat a phrase? Does your character stutter? Does he have an accent?
Your character drives the plot. You don’t want to bore your reader. Give your character a flaw to overcome and put obstacles in his path. Continue to increase the stakes. If you find your story is paced too fast, then slow it down with emotion. Good luck.