Give yourself just enough sherry or champers to have a warm happy glow (my Grandma was a master of this... though occassional had the extra glass or two too many [hic] - much to everyone's amusement... this tended to delay the dinner)
Give everyone a peeling task and a sherry (there seem to be a theme building).
Prep sauces the day before (or even earlier and freeze) - and pin up a reminder somewhere.
Use gadgets if you have them (an electric steamer can be left on without worry of boiling over)
Microwaves are handy for heating sauces.
A dishwasher is a godsend - otherwise ask a friendly guest to help keep things washed up as you go along.
Don't forget a turkey / roast benefits from resting before carving - giving the perfect time to use the oven to warm plates, keep veg and stuffing hot etc.
Often the alpha male/female likes to do the carving - great - let them get on with it!
Hot gravy helps if the meat has got cool.
If you have non meat eaters that will eat fish, wrap a whole trout or salmon fillet in tin foil (season with a little olive oil, lemeon joice, salt & pepper) and pop into the oven c 25 mins before serving. You can whak them on top of the roasties so no need for an extra tin/tray.
I'm sure there will be loads of other great ideas form other soon.