When I'm doing landscaping I think of a few things my art instructors taught me. First, uneven numbers rather than even numbers. Three trees together, or three points of interest, doesn't have to be trees, looks better than two or four. I also think of the color wheel. Do I want something that blends or stands out, colorwise, and in a garden green can almost be considered a neutral color.
Do I want something formal or carefree? Do I want cottage eclectic, (I think of the fabulous cottage gardens in England when I "see this"), or am I looking for something like Hampton Court Park Gardens, which are lovely and very formal? Do I want Versailles, or a tiny private spot? Or how about some of the rooftop gardens you see in big cities, which can be very varied with flowers, potted trees and fruits and veggies tucked in with nice places to sit and admire. Hmmm, I think I need to make a roof top garden. Here we have the Portland Experimental Rose Gardens which are cheek by jowl with the Japanese Gardens. So much to chose from!
I tend to use a lot of hydrangeas simply because the blue and white ones are cheap! If I had my endless funds though I know I could go hog wild.
Something I would like to see addressed in this thread is the use of ornamental rocks. I'm terrible at that! I never know where to put them or how to arrange them properly and I've often seen where there is a gratuitous rock just kind of stuck somewhere it doesn't quite fit in. I avoid using them because of this, so help would be good.