Every general advice is very simple which almost never repaired but are important to keep the line at bay Christmas days are:-
Limit consumption of bread (there are too many goodies and bread can be eliminated or restricted to a minimum).
Do not skip meals with the idea of “get home” later. You’ll reach more hungry and even dinner you may feel sick.
Do not deprive yourself, everything is great and try it in moderation (watch out for special dinner dishes, the occasions, it probably will be larger than normal and you can throw too much food). Small servings and all (you can always repeat the one you liked it).
Try to avoid possible carbonated drinks and alcohol controls.
Do not abuse sauces.
No need to skip dessert but eye! with traditional candies and candy tray season. Take one or two to better remove it from the table to avoid temptation.
Finally remember that a good walk after dinner will do you a great time and your stomach will thank you.