Change your volume. Use pauses or silence. Use expression - the feeling or tone of your voice that makes listeners sure of how a character really feels. Also use expression in your face. Use character voices when necessary, but also add your hands and body to the action.
Gestures help the listeners see pictures in their minds.
Remember, though you are telling a story and not acting. Don't get too ambitious. Look at the audience. Include them in your story whenever you can. To begin to tell your story, take your time.