The vast number of plants that exist boggles the mind and can be intimidating. In order to design well, you really only need to get to know a handful of plants that work well in your zone. As you grow more familiar with each set of plants you can continue to build your plant palette, adding more variety.
Commercial projects such as medians and planted areas around buildings will provide a good cross-section of hardy and low maintenance plants available in your area. As you see landscapes that inspire you or plants that you want to identify, take pictures and keep a file of what has caught your eye.
Though you can get by in design with a smaller palette of plants it is important to know the chosen few inside and out so as to be proficient in their usage.
Here is a template you can use to begin your plant list: Design by numbers-Personal Plant List Template
One way to get the list filled painlessly is to take a copy to your local wholesale nursery and ask them to assist you with identifying the top sellers. If certain plants are selling that tells us that they do well in the area with little coddling and will survive the climate. A retail-only garden center caters to homeowners who are going to be looking at plants in a different way and will thereby be purchasing in a different way. A wholesale nursery will have the inside track on what the professionals prefer to use. The pro is going for looks as well as durability.