Just to make yourself not feel so overwhelmed, I'd suggest taking ONE room, and totally doing it top to bottom! I'd start in the LR. IF it doesn't belong in there, take it to the room it doesn't belong in. Put it away if it has a place, and if it doesn't, put it into a pile in the room you think it should go in. Don't spend forever putting the things away or making places for them all, just focus on the ONE room. When everything is out of there that doesnt' belong, go thru and decide if you want everything left in the room (see PPs ideas about loving it, needing it, ect.). Next, vaccuum, dust, and then sit back in your nice LR, and enjoy the rest of the evening. I'd guess this would only take a couple of hours. Don't get into alot of detail on the cleaning (like dusting *everything* cleaning pictures frames, ect. Just get the basics, andm ake the room look nice). The next night, when you come home, put the things you bring into the house away, and choose another room. My second one would be the kitchen. Since my LR was cleaned, I'd start w/ the dishes next. (Don't cook supper this night, order in for less mess). Get a big trash sack and trash all of the boxes, mail, ect. that seem to find their way into your eating area. Do the same thing w/ items that don't belong in there. If it goes into the LR, make sure it is put away, but if it goes into another room, you can either put it away quick, or make a pile
It might take 2 nights to get the kitchen cleaned, depending on how bad it is (mine gets bad QUICK!). Just get all of the dishes done, and put away, all cabinets cleared off, and the floor done. Make sure that everything in there is something that you want or love. Sit back and relax!
The following rooms I"d do the same way! One at a time. When your house is back in livable condition, continue going thru the rooms, and gradually weed out things that you no longer deem necessary. A nick-nack is nice, but you have to find a place to put it, dust it, dust the shelf it is on, ect. REalize that this is a time investment, and make sure that it is worth it. You can always pack up keepsakes in boxes for sentimental reasons if you don't have a good place for them.
I'd also suggest getting fresh flowers for either the LR or kichen (or bedroom if that is one of the first things you do).
I'd spend an entire Saturday doing nothing but laundry! I do this often. I wash all of our bedding, then DH's clothes, kid's stuff, ect. It makes me pause and I can purge whateve clothing is looking worn, or that I"m just tired of seeing (like the stained Tees of my 2 year old). Make sure there is enough room in your drawers for ALL of you clothes. If there isn't, then get rid of more. I used to always be so far behind on laundry, but I got rid of anything I didn't wear often (read that at practically anything that needed ironed), that didn't look good on me, or that didn't fit right. I kept some stuff only b/c I did need some clothes before I could go shopping again. It really felt good, and I never have problems opening my drawers or finding anything, even if ALL of the clothes are washed dried and put away (I try to do this at least once a week!)