To my mind there are five golden principles for garden design.
1) Making a garden serve the functional needs of the person
2) Having good structural bones
3) Proportionally well balanced
4) Interest throughout the seasons
5) An adventure in colour and tone
The following photos I took on my trip to Australia. Notice how the background colour is just as important as the focal colour (You can imagine swapping it for another colour and notice how that would change the whole composition)