We have a few:
Christmas tree always go up on the anniversary of my grandmother's death in the second week of December. We all go together to pick the tree. When it comes to decorating it, I do it alone in control freak fashion with a glass of port or sherry and carols on, then the kids come in at the end and ruin it add their own decorations (stuff they've made at school or cheap tat bits they have picked out themselves over the years).
A few days before Christmas we have a big spring clean.
We always do at least one trip into the West End (we live in London) to visit Santa at one of the department stores, see the lights etc.
On Christmas Eve we have a sort of ongoing party all day with just me, DH, the kids and which ever stray relative is around. We start as soon as we get up - Christmas music on, the kids make Christmas hats/badges etc to wear, I put a spread of nice food out on the kitchen table and we all just help ourselves (and there is always mulled wine
). Really relaxing and gets us into the Christmas spirit. I always sneak off mid afternoon and have a wander down the high street, as I secretly love the 'last minute Christmas rush feeling'
.
We also have the Christmas Eve PJs tradition (DH doesnt partake, though
). I started it when our second child was born and was amazed to find out on MN that it is quite popular. We have new PJs and the kids get a Christmas DVD to watch, a Christmassy book (for their Christmas Eve bedtime story) eand some hot chocolate and biscuits to have while they watch the film. They absolutely love this tradition.
Christmas morning after we're all up, dressed, presents done etc, we always go for a walk. I love Christmas day walks. We usually go for a swifty in the pub, too. Love a glass of champers in the pub on Christmas day - nice to share the festive cheer! 
I've just made it sound like we are the most twee middle class family ever, haven't I? We aren't. I just love Christmas and force my excitement on everyone else. 