Nothing against bright fancy blooms, but here's the thing. When you design with only flowers in mind you may end up with a rag tag, bug eaten, scraggly mess. For instance, if you want only roses, what happens when you get black spot? All your roses get it. Ugh. Bare rose stems are not the prettiest part of the plant.
Check out a Japanese garden, take a walk and observe. What do you see? Form, texture, shape most likely. A little bloom here and there, but it's subtle and delicate like a piece of sushi topped with a tiny garnish.
Here are the basics: Use plants that have nice form and healthy foliage. Keep the leaves healthy if you can by getting hardy plants. Dwarf conifers are not only evergreen, but easy to grow. Mix them with rhodies, azaleas and lace-cap hydrangeas. Sound boring? It's not if you get good ones and keep them healthy and vibrant. Throw in a small patio tree with interesting bark or great structure like stewardia, or vine maples.
Does your garden look like a bomb went off in winter? Is it because all your plants are daisies, iris, and dahlias? Mix in some evergreens or shrubs with winter interest so you have something to look at other than your spigots and bird feeders come winter. Gardening is not just about April showers and May flowers.