Start with small areas that aren't frequented by NPCs, that way you don't have a risk of your deco being destroyed, and you can mess around and find a style that fits you, without having to feel obligated to decorate a massive map in a style you don't like just because you're most of the way done.
Here are some good ones to start with: Backwoods, farm cave, secret woods, a shed, a random room in your house