I absolutely love cooking Xmas lunch for the family. My suggestions to help things run smoothly.
Buy food on 23rd. You'll feel more relaxed knowing you have everything in.
Set the table the day before.
Get up an hour before others and prep meat and veg. M&S do great prepared veg that just needs heating in the oven.
If you want to have a starter, serve a cold one, ready made.
Ask someone to help you serve. You could always use tureens for veg and let guests help themselves.
Don't panic about washing up. Just fill the dishwasher and set it going. You can always empty it later and restock.
You don't have to have a hot Xmas pudding, supermarkets have some great desserts to serve straight from packets.
Hope this helps someone out there.