I'm struggling to empty my spare room at the moment! I've started making a weekly op shop trip taking at least a bag down each time - it's going pretty slowly though. Once i get through the small clutter, I'll be getting DH to take all of the furniture out, and then only putting back what we want to keep (probably only a bookshelf or two) We've let friends know that we're planning to get rid of a lot of stuff, and we've had a few offers from people who are willing to take excess furniture off our hands, so hopefully the rest of the house won't be too messy for long!
I try to follow the rule that if it doesn't get used, I don't need it. I struggle with things that were gifts, handed down from family, brand new or expensive but useless, and stuff that might be useful 'one day' - which covers 99% of the stuff in my house! So it isn't easy to part with a lot of it - but I've found that once I've gotten it out of the house I really don't miss it, and the extra space is worth it - good luck with it all!