Instead of setting aside a huge block of time to take care of months' or years' worth of clutter, take baby steps by throwing away only one type of item a day. And by throwing away, I mean recycling, selling, donating, or — as the last resort — trashing.
Clean out a space a day for 40 days, collect a bag of things from each space to give away or donate to a second hand store. Make your own list of spaces you can de-clutter. Or have a garage sale in 40 days, and donate what doesnt sale.