First thing that they might do is to update the appearance of the furniture in the room. This might be difficult to be done if you have limited budget. Thus, if you want to do this, you can try to do other tricks to change the appearance. For example, to repaint the furniture or use sofa cover.
This might be shocking to hear but the pros would not use a set of furniture that have matching appearance. What they actually do is to use individual furniture but making sure that they can complement each other thus make it appear matching even though the appearance is not actually identical.
Another thing that the pros usually do is to use window treatment on any window that available in the room. This is important since the window treatment actually will make the room appear softer with the use of fabric on the window. Of course, this also have something to do with the function of the window treatment that help you to control the amount of lights that entered from the window.
If you do not have any carpet, then you might want to try using rugs which will work as anchor for everything you placed above it. Furthermore, this item will also make the floor appear warmer and adding some color to the floor which is something hard to do. Other than those methods, here are other examples that you can do yourself.
image source : pinterest.com