If you buy, choose a day when the outside temperature is above 50 degrees to cart home your holiday treasure. And cover it with plastic bags from the store or bring your own box to keep the cold and wind out.
Hopefully your plant came with a tag which should give you basic care instructions. Often I take a photo of the tag just in case it gets tossed with all the foil or decorations.
When you first get home, carefully unwrap your plant and if foiled, cut some holes in the bottom of the foil and then place the plant on top of a tray so water will freely drain. Check for flying gnats and if present isolate the plant until they are taken care of. My recommendation is to break off small pieces from your outdoor water feature mosquito dunks and place on top of the soil, once watered in the larvae will be killed (the dunk contains "Bt," a very safe biological product to use). More - fungus gnats
Links with care instructions for some popular holiday plants.
Norfolk Island Pine
European Cypress and Lemon Cypress Potted Plants
Wishing you a happy, healthy December holiday season. May it slow down just a tad so you can enjoy more time with your guests. After they are gone, sit down with a 2016 seed catalog and dream of you know what!