Do you have any festive/holiday spirit when it comes to December? Not really.
When do you start celebrating &/or get into the mood? I don't really celebrate since I have no immediate family to celebrate with. I do spend Christmas day (and Thanksgiving) with a cousin and his family. Just a nice meal and watching their grandkids open their presents.
Is there anything special that gets you into the festive or holiday spirit? Depends. Some years, nothing will get me into the spirit. Other years, it might be listening to music or decorating.
December is the month I get SAD. My mother passed away on December 26th, so the holiday has never been the same since 1996. The last normal family Christmas I had was in 1995. In 1996 Mom spent Christmas Day in a coma like state in the hospital, not knowing anything that was going on. Dad and his brother spent time at the hospital while my aunt & I got some things ready for a cookout with my parents' friends at the trailer park they stayed in during the winter in Florida. Even before her death, December was a hard month for our family. 3 of my 4 grandparents died between Thanksgiving and Christmas (1971, 1993 and 1995). Nine years ago, the SAD was really bad as that was the first year I had neither parent (Dad had passed away in June). I try to keep myself busy so that I don't have time to think about the people I'm missing in my life. So I scrap, do jigsaw puzzles or read. That gets me through the month. While most people get SAD in January, I'm fine come January 1st.