Very minimal. Last year we bought a live tree (which was dead by February...) and decorated it with an odd collection of ornaments. Some were ornaments I made while growing up, like Oscar the Grouch made out of a black film canister and green pom pom, or a reindeer painted on an old fashioned clothes pin. Additionally, I have received an ornament from Santa every x-mas, and they were often related to what I was into at that age, so I have a variety of ballet, dog, percussion, and other odd ornaments that in some ways map my childhood. It wasn't the classiest x-mas tree, but it felt like home which was good for my first x-mas away from home. I also put up lights on the front of the house, and on some paddle cacti that I stupidly thought didn't have spines (I was SOOO wrong)!
This year we won't be around for xmas, and we have kitties with us now, so we'll skip the tree. I have been lighting candles when we're home because it feels so cozy, and we will definitely put up the outdoor lights.