I am by no means an expert, but here are the things I find help me:
I do a timetable which I follow religiously. Everything is on it, and I know if I follow it I won't forget anything.
I lay the table the night before.
I cook a gammon the day before. This gives some variety meat-wise, and if the worst happened and the oven broke we would still have something good to eat on Christmas day.
I do a cold starter and plate it up the night before, cling-film it and put it in the fridge.
I leave a 2 hour gap between the turkey coming out of the oven and serving lunch. The turkey remains hot, has time to rest, and I don't feel I have a massive cascade of things happening all at the same time.
I put boiling water in the serving dishes to pre-heat them, so that they keep the veg hot for longer, giving me more leeway in timings.
I buy ready-made gravy pouches from M&S. They are yummy and save me stressing about making gravy along with everything else I have to do. I do not admit to doing this to anyone.
I make some things in advance and freeze them, like mashed potato for example. Easily heats up in the microwave and saves prep time and a ring on the hob when everything is busy.
I always use disposable tins for the turkey, roasties, parsnips, sausages etc - it is my Christmas day too. Cooking it is enough without scrubbing tins.
Before I serve lunch I make sure that the dishwasher is full and on so that the kitchen isn't an absolute tip. This makes me feel a lot more relaxed.
The best bit of cooking Christmas lunch is that you know the house is full of lovely food and you don't have to cook for days. I love it!