If you don't buy ready made, make stuffing and pigs in blankets in advance and freeze.
If finances allow, buy as much ready made or pre prepped as possible.
Don't provide a mass of side dishes. Unless you have loads of oven and hob space, or e.g. a Hostess trolley, having everything ready on time still hot, and not soggy, will be a major PITA.
Best tip, though, is to work out timings backwards, starting from when you want to sit down to eat, including everything e.g. first turning the oven on for the roast, putting spuds on to parboil.
Then write it all out again in time order and stick it on the front of the fridge, or anywhere else it won't get lost or buried under kitchen debris - - and make sure you don't have so much Bucks Fizz/whatever that you forget to refer to it.
Oh, and a late dinner, not before 3, and 5 pm is better, is infinitely more civilised than 1 pm, when many people just won't be ready for it, never mind the morning being a major rush in the kitchen.
If having it later, don't bother with a starter. Nice canapés an hour or so before, works fine.