Work backwards from when you want to eat. Find out timings for everything you're going to cook, and write a timetable for putting things on the stove or in the oven. Example:
Put turkey on to roast, timer 1hr
Ham on to boil, timer 1 hr
Put potatoes to boil , timer 15 mins
Potatoes to roast, turkey out of oven, timer 20 mins
Baste pots, vegetarian main in oven, timer 10 mins
Pigs in Blankets, stuffing in oven, ham out of water to rest, timer 5 mins
Veg on to cook, timer 10 mins
Make gravy, timer 5 mins
Serve
Those timings are obviously not the real ones, that will depend on what you're doing, but I write it all out on a big sheet of A4 and blutac it to a cupboard door near the stove so I can check the next step and see what I need to do next and how long I've got, and so far I've never forgotten anything or overdone it. We often go really overboard with our Christmas dinner with vegetarian mains and sides as well as meaty ones, two types of stuffing, bread sauce, etc, but with a clearly written timetable I can manage it all with no stress.
Remember a large turkey can be left to rest covered in foil for a long time without getting cold, so you can get it out of the oven before you start trying to fit other stuff in as well, veg can be peeled and sliced the day before and left covered in water in the fridge.