Do a little research. Spend time reading garden magazines and then take note of favorite plants, tools, and tips in a garden journal or folder. You'll be more likely to buy plants that thrive and garden supplies that are truly useful and needed.
Be realistic. Know what you're looking for when you go. If you give yourself a list or budget, it's easier to stick to it and not make unnecessary impulse purchases.
Shop during off hours. A beautiful spring Saturday morning when the garden center is swamped is not a good time to ask garden staff questions or shop in a leisurely, thoughtful way. Friday afternoon, when fresh shipments of new plants are often just in and the crowds are smaller, is a better time.
Stop in often. Good garden centers have a variety of merchandise and plants that they are always rotating in and out. You'll learn more about early spring gardening, for example, if you visit the garden center in early spring and see what's blooming and what's in. You'll learn more about fall gardening if you visit during the fall.
Talk, talk, talk. Ask garden center staff questions -- they'll do their best to help. And be as specific as possible. Bringing in pictures or drawings of your garden is very helpful in communicating what you need.
Read, read, read. The label, that is. The basics are all on the plant label or on the package, but it's amazing how many people don't really spend a moment studying them before they make the purchase.
Save the receipt. Many plants have a one-year guarantee but a receipt is usually needed. Tuck it into that garden journal or folder.