Most of my tips have been gleaned from here, so you might recognise a few:
Cover an open cardboard box with wrapping paper, use it to chuck used paper in as they dc are unwrapping, that way, when you take photos of the dc and the tree etc there isn't a nasty old binbag in the pictures.
Have a Christmas cupboard where you keep all your: Christmas crockery, napkins, table decs, candles, tablecloth... all the paraphernalia for setting the table and decanting the nuts!
If you are having a big even one day (either in your own home or going out), make sure the day before is a relaxing sloth day.
Make mince pies and freeze them - done mine already!
Have somewhere in your handbag or at home, wherever handy, to put all your receipts in. This can be handy for exchanging presents, swapping a jumper for a bigger on, for example, replacing something faulty/broken. And it can also help you tally up haw much you've spent and perhaps help you budget better next year.
Have food in for light meals: salmon, biccies, vegetable soup.
Don't forget to eat fruit breakfast is the best time to stuff your face with satsumas and have a banana. Drink plenty of water.
Fake-plan some days: use these days as down-time, you can only visit so many rellies/neighbours.
If you get anything free during the year, like make up/perfume samples, put them together in a little washbag and have handy as a 'travel kit' gift just in case you realise you've forgotten to buy something for someone (or need to reciprocate). Mean, but handy!
Put a little cash to one side for the January sales for: paper, tags, bow, tealights, cards... etc.
Do Secret Santa with people - doing it this year with friends AND family as we're all bloody skint and know Christmas is really for dc. Finding two really nice gifts will be a lot easier than 15 slightly crappy ones!
E-bay things you don't want/need anymore (you or dc) in September/October, then spend the cash you get on present for this year or a trip somewhere or... well, whatever you like! Someone might be looking for what you're selling for a present for someone and snap it up quickly. Those months are also great for getting Playmobil/Lego/Brio etc stuff cheaply on ebay as the prices will rise before Christmas.
Prepare a First Aid Kit containing: plasters, antiseptic wipes, painkillers, germolene/savlon, light bandages, hangover cures, Rennies.
I may think of some more, I have written down some from this thread already, thanks 