Diana has been planting pots for me for 10 years. She starts with a square of landscape fabric over the drain hole, and adds drainage material to 2/3 of the pot. Another layer of landscape fabric prevents the soil from sifting down into the drainage layer. We use a topsoil/compost mix for pots. Soil-less mixes are great for professional growers, as it is sterile. Professional growers know how to water and fertilize properly. I like real soil. We mix in osmocote, a time release fertilizer; the rate of release speeds up as the soil temperature goes up. Apply according to directions. We go for that lush look; we pack the plants in, so they look great from the start. Later, we groom the pots. We remove excess growth underneath to keep the air circulation good, and the possibility of fungus low. We cut back the dead flowers and leaves. We may even shape the overall composition by trimming and cutting back. Does she not make it look easy??
Spring plantings do look great in old crates, wood boxes, buckets and baskets. Landscape fabric can help hold the soil where you want it; coir sheets can be cut for boxes with big open spaces. Coir is a mat woven from the fibers of the hull of the coconut; it is sometimes called coco fiber. Have at planting some pots.
Spring flowers have that spring-fresh texture and color guaranteed to shake winter off of you, and your spirit. No summer flowers have the blue of clear sky blue pansies, and blue lobelia. Alyssum, the crisp white smell of spring, also comes in lavender, red violet, and purple. Ornamental kales, cabbages, Angelina sedum and coral bells have robust texture and leaf color. Lettuces, parsley, and gold oregano hint of the vegetable garden to come. Yellow and vanilla butterfly marguerites are quite cold tolerant, as is the chartreuse leaved Persian Queen geranium. Annual phlox performs beautifully, blooming on into the heat of the summer. Violas come in all kinds of colors, and bloom profusely. Fresh cut pussy willow twigs, yellow twig dogwood, and artificial grassy stems provide scale and height. Pots of hyacinth, daffodils, and tulips can also be popped into a pot for their duration.
Spring is a season like no other. Give some time to enjoying it. Spring pots are a perfect for a collection of lettuces that will spruce up your salads. A collection of spring pots also helps considerably to stave off the impulse to plant summer pots too early. Most summer annuals despise cold soil and cool temperatures. For everything, the right season. Plant your spring. 
Tools are useful. This does not mean they are precious. My landscape plans are a two-dimensional description of a sculpture which is to come. They are not an end in themselves. I go over them with my superintendent; we do a layout. That plan usually ends up in a lunchbox, a back pocket, or after it is irreparably wet and mud smeared, in the trash. They are a means by which to communicate.
There are computer programs which help projects to get drawn quickly. I use them to draw very complicated structures. They are very useful in detailing changes to this and that-without having to redraw everything. But I am most interested in the evidence of the human hand. I draw by hand, as that drawing is part of a process which is distinctly my process. My clients find out that as I respect the evidence of my hand, I have the ability to respect theirs as well.
I am happy to discuss at great length my process for designing a landscape. I plan to go over this in excruciating detail, for those who can last! Tools and skills are just that-nothing more, and nothing less. I would reveal anything and everything-and still be completely confident that I have something worthwhile to offer. I have made a living almost 25 years, designing. Enough said.
I have plenty of clients that are eminently able to be on their own. Not professional designers, they shortchange their talent and heart. It has been my good fortune to have clients of all kinds, with talent and heart. I know this better than most.