This part is fun.
1. Vacuum your floor and lock dogs and children in the other room.
2. Get out your stash and dump it.
3. Roll around a little just to get it out of your system.
4. Put all the balls of the same type of yarn together so you know how much you have of each.
5. Consider sorting them by weight so you can see, for example, how much sock yarn you have, or how much laceweight, and so forth.
6. Anything that you have less than a ball of, put in a separate container or bag where it will be safe. You'll deal with these leftover yarns later (though feel free to dip in for trims and embellishments throughout.)
7. If you feel so inclined, go ahead and photograph the stash and put it on Ravelry. Or make a list. You don't really have to do these things, but they will definitely help if you don't feel like leaving your stash out on the floor during the next few steps. Doing it all at once certainly has it's advantages, though.
I felt bad for the dog and was too lazy to vacuum so I put mine on the table. Heh...
I have this:
Plus this blurry wad of overflow here:
And this huge amount of "OMG IT'S ON SALE" ambrosia from knitpicks:
(and in case you're wondering, this is what's in the background:
I bought a kit for $1.50 at a thrift store and then just sorta went my own way with it. I like him! )