Balancing the repetition and the contrast is where the art takes over from the science. Movement deals with traffic flow, how you will move through the garden. It also deals with how your eye will move through the garden, and how curving sweeps of plants and partially hidden views will draw interest. Depth is created by using low, medium, and tall plants, or by using various shades of the same color. Harmony is achieved by repeating plants and patterns to provide a unifying effect.
Contrast provides interest and excitement.
These accents become the focal points. Balancing repetition without monotony, and contrast without confusion, is the key element for a peaceful design. You don't need absolute symmetry, just implied balance. Color is vital, including using contrasting shades and textures of green. Seasonal progression of blooms, foliage colors, and bark gives a year-round interest to the garden.