I love decorating my villagers houses, although it can get a bit tedious! What I do is order a bunch of stuff that'll look good and keep it in my closet. Then I do this:
When a villager is inside their house, I fill my pockets up with flowers except for the item of furniture I want them to have (so they can't give me a bunch of ugly shirts). Then I go inside their house then save the game, then repeatedly talk to them. Usually at some point they will ask to buy/trade for the furniture I'm holding, and I accept. Then when that's over I go outside, then go back in again and see where they've put the new furniture. If it's somewhere good, then I save, if it's badly placed or has replaced something good, then I quit without saving and do the whole thing again. I also do that for when villagers ask me to find furniture for them, so I can make sure they don't put it somewhere dumb in their house!
You can also do that process with shirts instead of furniture, once they buy it off you they will often change into it in front of you. If they don't, quit without saving and repeat.
It sounds long and boring, but it actually didn't take that long for me, and it's worth it when you get their houses looking awesome and you know you've given them somewhere really nice to live :-D
