Don't feel that you need to apply every principle to every part of your plan. Having an understanding of these principles can help you generate ideas & increase your creativity.
Whether you plan to "borrow ideas" or plan on generating your own landscaping design, you ought to have at the least a basic understanding of the principles of landscape design.
Unity should be of your main goals in your design. It may be better understood & applied as consistency & repetition. Repetition creates unity by repeating similar elements like plants, plant groups, or decor throughout the landscape. Consistency creates unity in the sense that some or all of the different elements of the landscape fit together to generate a whole. There are many services for lawn care in Maine and landscaping that can help you achieve desired results.
Great landscaping lies in the eyes of its creator. So, while the principles of landscape design are great guidelines to follow, don't feel like they are the "have to rules" of landscaping. Abstract & creativity are allowed.
A lovely example would be in the use of accent rocks & boulders. If you have ever seen a landscape design that had several different colors & sizes of boulders, then you have seen that unity wasn't created by this particular element.
Unity can be created by the consistency of character of elements in the design. By character, I mean the size, height, texture, color schemes, etc. of different elements.