The label should include the common name and Latin name of the plant. Since common names vary considerably, researching the Latin name can give you a more accurate description of the plant.
Make note of the USDA or Sunset zone that's listed on the label. Don't buy a plant that's not rated for your zone, unless you want to do a little experimental growing — for example, if you live in Zone 6, you may want to take a chance on a plant that's hardy only to Zone 7 by putting it in a protected area.
If the label doesn't mention heat tolerance, find out the southernmost zone the plant can tolerate (you can research this easily at home by Googling the Latin name).
Note the recommended planting conditions (type of soil, light requirement, water needs, mature size, etc.) before you buy.
Be sure you can offer the recommended spacing so the plant has room to grow out as well as up.
A plant that's referred to as “tender” should be treated as a houseplant unless you live in a warm climate.
"Full sun” typically means at least six hours or more of sun.