Some rules I'm developing:
1. When you feel yourself getting tired, stop what you're doing and straighten up a little before you totally run out of steam. If there's trash on the floor, sweep it up and throw it away. Make sure at least one two-foot square spot looks orderly, even if it's fake order you've created. You need to be able to walk into the attic (basement, pantry, closet) the next day and not feel completely defeated.
2. Lego is not sacrosanct. It's okay to throw away the occasional piece of Lego. No one's ever putting those kits together again anyway.
3. Remember how many years you have a) recycled; b) carried your own canvas bags to the grocery store; and c) composted. You have earned a small, guilt-free spot in the landfill. There will be items that you simply can't recycle, freecycle or give to Good Will. Toss them into the trash and move on with your life.
And a quote that motivates me in this effort to simplify and clarify my surroundings:
"It is the main earthly business of a human being to make his home, and the immediate surroundings of his home, as symbolic and significant to his own imagination as he can."
Which is to say, to some degree I'm considering this decluttering campaign an art project.