At Christmas I frequently prep nearly everything except the meat the day before.
Parsnips and potatoes, peeled, par-boiled and roasted until nearly cooked but not crispy. Carrots, peeled, chopped and cooked until just under-done. I don't cook any brassicas the day before (cabbage, sprouts, broccoli) but I do prepare them ready for cooking. If we have peas they are frozen and only take a couple of minutes anyway. Swede, cooked and mashed. Red cabbage, braised and ready to go. Cauliflower and leeks, if having either in a cheese sauce cut and cooked. Cheese sauce made and dish assembled.
Parsnips and potatoes then go into the oven when the meat comes out to rest, as do pigs in blankets, stuffing (if separate). Meat comes out at least 20 minutes before it needs to be carved, and is covered in foil and a tea towel to keep hot. Carrots, swede, red cabbage go in the microwave just before we need them. Cabbage/sprouts/broccoli have to be cooked last minute in my opinion. If the sprouts or broccoli are being roasted then they need to go in the oven at the appropriate time, but I don't usually roast them. If I was doing something in a cheese sauce just reheat on the day, either in the oven or the microwave depending on which had more space.
Gravy is not prepared in advance, but if using stock then that is got ready beforehand. Bread sauce or any other kind of sauce I would get ready the day before and reheat if it's a hot sauce. Yorkshire puddings (frozen - I buy them but you could make them yourself and then freeze them) go into the oven last minute.
What I do do, is to sort out all the serving dishes/implements the day before and label them so there's no last minute scrabbling around to find a dish for the stuffing only to find it has been used for something else. We are a serving dishes on the table family rather than a dish up in the kitchen family. We are also lucky enough to have a separate dining room so the table gets laid and decorated at least the day before... It could be two days before. Cold sauces etc. get put on the table early on the day, covered.
Basically - I do as much as I can in advance so there is less work and stress on the day. If it can be done the day before, I do it the day before.