According to the text what is one of the easiest ways to create a sense of unity in an artwork

Unity is a quality of wholeness and oneness that is achieved by the proper use of art elements and principles. Understood as a complete opposite to the notion of variety in art, unity is both an idea of calmness, simplicity, or repetition of the same[1]. On the other hand, the atmosphere of unity is present in gestural and expressive paintings as well.