When I'm stumped about why a room isn't working, I'll often invite a friend over to get their opinion. While I'm in a particularly fortunate position given that a lot of my friends have great ideas about things I can do in my space (believe me, it can have a downside too!), I feel pretty confident that the opinion of your friends will be just as valuable.
Ask for their opinion: Whether it's a fellow decor-obsessed friend or just someone who spends a lot of time in your home, they've probably mentally redecorated it at some point. While you may disagree with many of their opinions, pay attention if something comes up repeatedly.
Notice how they use your space: Look to where people gravitate when they come into your home. If everyone's always vying for one corner of the couch or no one ever sits in the living room, pay close attention. Maybe the chair in the living room that always gets filled last is actually uncomfortable.
Notice if they move the furniture: If you're always rearranging the furniture after a party, stop. Your guests may actually have unconciously told you something about what works in your house and what doesn't.
You find yourself apologizing for your furniture: If you're always explaining why something isn't working correctly, or worried that something make break, make a mental note to fix it or replace it.
You have whole rooms no one ever goes into: While they may be well-decorated and comfortably furnished, if they don't work for your lifestyle, they're just, literally, taking up space. Same with any items that don't get use at least once a year.
(Image: Andie Wurstler from The Fleet Family's Modern Craftsman Mix)