We just moved. :-) I understand what you're going through.
The trick is ONE ROOM AT A TIME.
This is a wonderful opportunity to get organized and purge the junk.
Post the big junk on Craigslist. Check out what comparable items are going for so you don't try to sell it for some ridiculous price. If it's not worth buying, post it for free. There are lots of folks who will haul away whatever you have. We made about $700 selling stuff that was collecting dust on Craigslist.
Also, check out your local Freecycle group (yahoo Groups). Sign up, then post what you have and folks will come and haul it off. Seriously, people want the weirdest stuff! I had someone come and dig up daffodil bulbs when they were getting out of hand. And some other folks came and hauled off some old cast iron pipes from the back yard.
For the rest? Do one room at a time. Trying to do it all at once will overwhelm you.
Pick one room per week. Get some boxes from the local produce departments. Pack, toss, sell, donate. Pack what you want to keep, toss out trash, put stuff to sell in a pile for a garage sale, and whatever doesn't sell at the garage sale? Donate it to charity. And if you don't have time for a garage sale...sell what you can on Craigslist (they have a very easy to use app), and donate the rest to Goodwill or the Salvation Army.
A few helpful tips: Call your local trash company and rent a dumpster. It's so worth it. I spent $125 to have a dumpster for a month...and tossed TONS of junk. I didn't even realize I HAD that much junk! The trash company dropped it off where I wanted it and picked it up when I was done.
If you haven't used it in over a year, and know you won't use it in the next year...get rid of it. Give it a new home. Sell it. Someone will adopt it and love it and use it. Just because you spent money on it or Great Aunt Ina gave it to you doesn't mean you should keep it.
You don't have to keep EVERY keepsake. One or two items will help you cherish Granny's memory every bit as much as 50 items. So ask the family if anyone would like to share in the memories. If not, keep just one or two of those items...and give the other 48 a new home so they won't be cluttering up yours.
Use one room to stage all the packed up items. Garage is easiest. Clear out one side and start putting everything you pack from each room in there neatly so it's ready to put on the moving truck. That way you can EMPTY rooms as you go through them one-by-one.
Lastly, find a cleaning company who will do a move-out-cleaning for you once your house is empty. It's SO worth the money. I found a local company that is licensed and bonded who cleaned my 1200sf house top to bottom for $100. Which meant that I didn't have to. They even cleaned the fridge and oven. :-)
Hope that helps!