PLAN: Try and pace yourself leaving as little to do as possible towards the moving date.
NOTIFY your legal adviser, so they can obtain your deeds and check all is in order with your title; avoid nasty surprises.
SORT and clear out unwanted items from your old address, giving yourself time to wisely dispose of these things, e.g. by gifting to family, selling at auction, car boot sale, charity shops etc (Remember the contents of your loft, shed, and garage!)
PACKING always takes much longer than you think, try not to have anything left to do on moving day that you could have done before: look for packaging materials well in advice, e.g. collect boxes from supermarkets, find/buy plastic bin liner, newspaper etc. Mark what is fragile appropriately.
TAKING your favourite plants with you, or cutting? Pot them up at the appropriated time of the year (i.e. a year in advance if possible) so that the garden doesn't look denuded when prospective purchasers inspect.
SURPLUS stocks of domestic oil, firewood etc? See if you can negotiate selling the surplus to the purchaser, or run the supply right down.
PETS, OLDER RELATIVES LIVING WITH YOU AND CHILDREN. Don't forget to make suitable arrangements for them: ideally leave with someone else and collect when the move is completed.