Working 12+hour days is normal and there are at least 5x as many customers than in non-holiday seasons. Don't be a dick, and follow these suggestions.
  1. Know what you want
    Don't hold up the queue if you are unsure
  2. Be polite
    Working retail at Christmas is stressful enough without you being snappy or rude
  3. Come in early
    Don't come in at closing time and expect workers to stay late because you didn't plan ahead
  4. Don't cut in line
    Everyone wants to be out of there as much as you do, you're not special.
  5. Don't yell at me if something is out of stock
    I am not the manager nor did I buy the last one just to piss you off....take your ire elsewhere
    Suggested by @penguinchrissy
  6. Ask for help if you're stumped about what to buy for someone.
    Most sales associates will actually keep your budget in mind and try to help you pick something great (provided you're generally polite and treat them like a human being).
    Suggested by @ohwowawesome
  7. Please don't unfold every neatly folded shirt resting above that XL shirt that you want. It took 30 minutes to fold all of those. You can really easily look at the tags outside and lift the top ones!!!
    Suggested by @stephaniehail