Four textures bring more interest, even if it's all in the same color. While most of it's probably paint, there's sure to be wallpaper and wood paneling in there, too. So if you've got an unused room, start by getting rid of those white walls. Proportion, symmetry, scale, layout, etc. I got the tallest, widest wall unit, a huge ottoman and a room-sized area rug.
Art is also either overscale or grouped.
The rooms in your photos will have matching scale and good proportions. And while you might see a delicate bench topped by a massive painting for dramatic effect, you'll never see a big sofa topped by a few wimpy plates or prints. Interior designers know the exact science of scale and proportion. A good one can tell you, over the phone, what size of bed and dresser is going to work in your bedroom. It's advice worth following, but you can get by with a careful eye-balling as you decorate.