Look for instructions on temporary handling.
These are usually included as part of the planting instructions. Handling will vary from plant to plant, but you'll find a few general rules for different types of planting stock below

Plant as soon as possible.
Until you do, give the planting stock proper care to maintain its viability Follow the instructions provided with your shipment.

General Rules for Temporary Handling Seeds: If your seed order arrives early, simply store them in a cool, dry place until it is time to plant.

Bulbs, Corms, Rhizomes, and Tubers
Keep bulbs such as tulips and daffodils in a cool, dry spot with good air circulation until they can be planted. Remove them from the packaging and spread them in a single layer. Keep them dry and avoid temperature extremes. The ideal time to plant such bulbs is in the fall, after temperatures have permanently cooled, and before the onset of winter freezes that harden the ground. You don't want to plant them too early nor wait until the ground is unworkable. And remember, always plant bulbs pointy end up.  In contrast, dahlias, lilies, and other bulbs that are not winter hardy, should be stored in the dark (in a closed box) and lightly sprayed with water occasionally to keep them moist until planted. Rhizomes, such as irises, can be kept in their packing material, as long as the shipping carton is opened. Store them where they receive some light, but are not exposed to direct sun or wind.

Green Plants
Green plants (in nursery pots) are in their growth cycle and require the most careful handling Remove them from their packaging, water them, and place them where they receive the proper amount of light according to specific instructions, and the proper range of temperatures, especially if they are tender plants. Stock in small pots can dry out quickly so keep close tabs on them and plant as soon as possible. For container stock planted at mid-summer, cut back tops by one-third to prevent die-back Bareroot Stock Many perennials, shrubs, and trees are shipped bareroot (without soil) in a dormant state. Until planting, keep the roots in their protective wrapping (plastic, newspaper, burlap and wood shavings). Moisten them frequently and keep them from exposure to direct sun. The greatest danger is excessive drying. Before planting roses, shrubs, and trees, soak their roots in water for a few hours. Carry them to the garden in their water bucket and plant them directly from the water to avoid any drying prior to planting. If you are unable to plant for a longer period (a week or more), it is advisable to "heel in" bareroot plants. Heeling-in is a form of temporary planting. Dig a V-shaped trench deep enough to hold the roots. Place the plants in the trench so they are sitting at about a 45� angle, and cover the roots with an equal mix of builder's sand and peat moss. If the soil is workable, you can use it instead of the sand/peat moss mix. Keep the plants well watered, especially if temperatures are warm, until you are able to uncover and plant them.