Ugly sweater parties usually happen in early to mid-December, so order by late November to allow time for shipping and exchanges. Popular designs and sizes sell out fast.
Decide on the type. Knitted sweaters are warmer and look more authentic, while printed sweatshirts are lighter, cheaper and better for crowded, warm parties. Light-up sweaters win contests but need batteries; check whether the battery pack is removable before washing.
Fit varies a lot between brands. Check the size chart, and size up if you plan to wear a shirt underneath. Read the care label too: many novelty sweaters need hand washing or cold water. If you are buying for a group, order everyone's sweater at once so the designs arrive together.
Matching couple and group sweaters are popular for photos and team contests. For something to wear on Christmas morning, see matching family pajamas, and complete the look with Christmas socks.