When I stared my landscape design company I developed relationships with local nursery's and got the opportunity to spend some time with their customers. Best of all I got to witness how they shopped and what factors were important to them in selecting plants. I also got to see first hand how the nursery managers would set up the store and their rational. It seems that most people will buy what is flowering and in season.
Every season the flowering plants were rotated to the front of the store, placed on end caps and the plants that were not "in season" were located in the endless rows at the back of the store. When I started working on some of there customers yards it started to become evident what seasons they were buying plants because everything blooms at once.
I call this the "impulse gardener", and explains why so many of my customers are not happy with their landscape and need a designers help. With just a little research and education any one can have a yard that offers interest from Spring through winter.
When I start a design project winter is the first season taken into consideration. This helps to establish a foundation for the rest of the plantings. Typically this will include evergreens, ornamental grasses, Hardscape, and boulders. Not only will these elements create interest but a backdrop for the rest of the year.
Next step in my process is developing height variations, contrasts, and foliage color. Usually this will be deciduous shrubs and some broad leaf evergreens. I especially find value in combining plants of dark foliage color like Diabolo Ninebark with brighter golden hues of Golden Vicary privet, or golden mock orange. But remember that dark colors will receded and bright colors will come forward.