If possible, you take yourself away from all the festive stuff, until the year you can in part join in.
This may take years .....or just one!
But, if for any reason it is very hard for you to be around people, be kind and look after yourself...and just go for the day.Or a few.Until it has all died down.
My then 17 yr old daughter died suddenly and unexpectedly in 2010, 2 weeks before christmas. Since then I have not been able to celebrate christmas. It has been hard on the family, as usually we celebrate with my in-laws, and my mother-in-law really loves to go all out at christmas time. She treats christmas as more important than birthdays. I don't want to ruin it for her, but both my husband and me feel unable to join in, and just can't get happy or excited about it. My son, who was the twin of my daughter, doesn't want to do anything either. He just wants to ignore it. I think we would all prefer to go to bed on the 24th and wake up on the 26th.
But that doesn't mean we don't want others to enjoy christmas. But I find it so hard when other people say "Merry christmas". I usually just smile back and say "and a happy new year" or something along those lines. Christmas is just an unbearably sad time. It would make it a lot easier if people just didn't say "Merry christmas" to us. We can still talk about the weather, having time off, vacation plans, all the usual stuff of conversations, just nothing about christmas because it hurts every time it is mentioned. So that is the hardest part for us.
As for the rest, we just get on with our lives as if it was a normal weekend. This is the easiest way we have found of dealing with it and not being overcome by our grief and sadness. We will still shed a few tears on christmas day, because we can't avoid it, but not having to be jolly is easy when we aren't having to participate in celebrations or other joyful activities.
I play the music at my local church so have to do that (either Xmas eve or morning), but then try to treat the day as another ordinary day, as I'm often alone for it.