How many are you hosting?
What do they expect? (Turkey, ham and spiced beef; 1 bird, or happy with any roast meat?) ("Must make" bread sauce, or "it's ruined" if there's no cranberry, or happy with whatever is put in front of them?)
Would any bring a dish (starter, or dessert, or a side/2, cheeseboard, etc)?
Would any give any help out in the kitchen in advance or on the day?
Are they only visiting for the day or are there visitors there overnight as well?
Do you have freezer space to do things in advance?
Do you LIKE cooking, or would you prefer to let someone else have the hassle? Or is it more the prepping part, the cooking part, the hostessing part or the cleaning up part (or any combination of those) that you are worried about?
(Slightly irrelevant but some indication of available time - do you WOHM or are you a SAHM?)
Like Mummysh0rtlegs, I prep a fair amount in advance whenever I am hosting (although it's only ever us 3 for Christmas Dinner if at home - but I do host on Boxing Day and do prep ahead for Christmas dinner too).
I like to have at least good chicken stock, if not some turkey stock (I may do a joint for Thanksgiving in November) in the freezer.
I sometimes get the veg prepped and blanched ahead of time and frozen, and the potatoes too.
I make the herby butter for the turkey on Christmas Eve, or even earlier if I get the time (it can be frozen).
I also make the stuffing, if it's bread stuffing - and often do that ahead of time and freeze. That's fine to do. DH though likes to use sausage meat in the stuffing, so that's his job to boil and then make the stuffing (including the traditional phonecall to DMIL to ask how to cook the sausage meat!) on Christmas Eve. Even just buying breadcrumbs or making them as you have crusts that won't get eaten is a good step and both of those options are perfect for freezing.
I always clean and peel the veggies on Christmas Eve, leaving potatoes in pots of cold water, carrot batons in another pot of cold water, sprouts in another, but parsnips need to stay in an airtight container with no water (or they get slimy) and the same with onions/garlic if using.
Decide what you would like to serve - a plate of smoked salmon may be a lovely starter but more tricky if larger numbers and soup may work better there. Or you could have something plated up cold ahead of time - or easy to plate in a hurry. Pate could also work well.
If oven space is an issue, cook ham the day before and serve that cold or steamed to reheat. Use a tiered steamer to cook a couple of types of veggies. Cook the bird, and have everything else ready to throw into the oven once it comes out to rest as that needs at least 30 minutes and can be an hour or more - just pop some tinfoil back over the bird and cover with a couple of folded bath towels to keep it piping hot!
Do a veg or 2 on the hob, while potatoes roast and maybe some roasted root veg. But sprouts are great steamed and then tossed with bacon, or some steamed broccoli, or even frozen peas just quickly boiled at the last minute (petits pois only take the time to bring water back up to the boil, I find).
Have the gravy made in advance (whether the day before or frozen), in a pot on the stove - just make it a little thicker than you would like it, and then add in the turkey juices to it before serving.
Once you have a roast potato for everyone, do a large pot of mashed potatoes (or even herby versions and call it potato stuffing) on the hob. Or have a second tray of smaller ones already parboiled to go in as you take the rest out and all sit down - which will be ready for anyone who wants seconds.
Remember you can use your microwave to cook or reheat things.
And while you think about what you can do ahead of time easily for yourself, and what you want to buy in, think about what will save YOU the most in terms of energy. And what will make the biggest impression as well - so you may want to buy the bags of potatoes that are pre-peeled and ready to cook, or you may want to buy a "WOW" inducing starter, or ready to plate desserts, instead of the whole thing. Or you may decide that it is worth the cost to YOU to buy it all in - just bear in mind the cost per person and overall to feed everyone, and the hassle of ordering and collecting/getting delivered in those manic few days.