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. Before you put the first plant into the ground, you should analyze the property for it's usage, it's optimum growing conditions, and it's mood. This checklist will help you judge the property and its needs. Screening Future expansion, pools, garages, etc.