Throw away everything you can - old bills, broken this and that that you never got around to fixing. Save the ragged towels, old blankets, etc - they can be used as padding.
Sell what you can in yard sales, rummage sales, etc, or donate good used items to charity, Goodwill, etc.
Box up and label everything you don't need for day to day living. Label the box with the contents, and what room it goes to in the new house.
Make up one or two boxes with basic housekeeping supplies to be unpacked first at the new house. This will have things like toilet paper, paper towels, cleaning supplies, toothpaste, new toothbrushes, towels, wash cloths, paper plates and cups, plastic silverware, kleenex, a few spare light bulbs, aspirin, any routine medical supplies, etc. This is the place to put stuff that you don't want to search for in 200-some boxes of stuff. Then keep these boxes with you, or make them easily accessible on the truck so that they are unloaded first when you arrive at the new place.
Make a list of all the businesses that need to be contacted - utilities, doctors, dentists, optometrists, veterinarians, banks, credit card companies, pharmacists/chemists shops, etc. Go through all your recent bills to see who you've dealt with to get more for the list. Write down their name, phone number, address, account number, etc, so you can contact them and file a change of address, cancel services, etc.
Find the address and phone # for the utility companies in the new area, so you can start services there also.
Notify the postal service of the change of address, and ask that all mail get forwarded to the new address.
Contact the vet for advice about moving pets. Dogs may be OK for the ride. Cats may get very upset. Ask about tranquilizers for the animals, and test them ahead of time if you get them. A friend found out the hard way on the drive to the new home that his cats were allergic to the tranquilizer he was told to use.
Make arrangements for the moving company, or reserve a truck if you're moving yourself.
Collect cardboard boxes from everywhere you can. Grocery stores are good sources.
Above all, understand that it can be a stressful time, and try to not fret over the small details. Roll with it, and be prepared to say, "I'll worry about that later".