Pack up ornamental things, "good" china and glass, winter clothes, Christmas decorations, entertainment collections (books, CDs, DVDs, less used gaming systems etc) early on. Keep things in more daily use until later in the process.
LABEL boxes, as someone said, TOP and at LEAST 1 side (I generally aim for 2 if possible). A room (for destination in new house) and an idea of contents (single word).
At the top of each box, just before you close the lid, put in a list of everything in that box. It means, when you are opening boxes again for "the corkscrew" or "my favourite turquoise jumper", you can see if it's in that box without taking everything out. But if you DO take something out, cross it off the list!
If possible, especially if you are relegated to no lifting, do that list twice and keep a copy in a folder to refer to, and number each list to a box number.
Thick black markers are your friend!! Buy at least 4!! To label, and also to indicate which way up if necessary on some boxes.
Buy at least 2 RED markers as well, to mark any FRAGILE boxes (and ONLY use those on Fragile).
Buy a tape dispenser and a few rolls of brown packing tape. Let no one have it except the person doing the master lists and sealing the boxes.
Box for first opening in new house:
Kettle, mugs, teabags, jar coffee, sugar, 2 packets of biscuits, roll of bin liners, couple of glasses (for water etc), plates and cutlery for 1st night's takeaway dinner, (corkscrew/bottle opener?, tin opener?) packet of Jcloths or similar, scouring pad, cleaning materials (windowlene, spray for cleaning surfaces, spray for bathrooms, bleach, washing up liquid etc), couple of pairs of rubber gloves, roll of kitchen towel, at least 2 toilet rolls, hand towel each for kitchen and any bathrooms, couple of tea towels. Possibly some plastic glasses and cutlery, paper plates etc if it makes it easier on night 1.
Also the tools someone mentioned above should be easily accessible.
Methodically work through rooms, starting with least used. Go through cupboards, and be ruthless on throwing out or going to charity shop as you pack, not afterwards.
Bags for dumping go straight away to bin or organize in shed for a dump run.
Bags for charity shop should be taken regularly and not allowed to build up (they will only take so much in a drop anyway) - so every day or 2 send someone off to deliver those.