Degree of Formality
Certain things tend to go with each other. Silk, silver, crystal, brass, china, oil paintings in gilt frames, and draperies to the floor have an affinity for each other for example. Leather, built-in bookcases, old books, paneled rooms, coffered ceilings, and dark wood are another group of things that go well together. A third such group might be heavy linen, polished cotton, glass and metal tables, woven baskets, and wicker. There are the usual exceptions, but things that go together tend to have about the same degree of formality. Their color and texture are important, too.
Light vs. Dark
Most people are happiest living in rooms that are bright and sunny in the daytime and are softly lit without glare or sharp contrasts in light at night. In most rooms, lamps and indirect lighting is the way to go. Window treatments that leave most of the glass in windows uncovered when they are open during the day are good for letting sunshine and pleasant views in and give your home a cheerful feeling.
How much sun a room gets needs to be taken into account when choosing paint. If a room gets a lot of sun, and you like the look, a dark color will probably work. If the room is on the north of your home and has few windows, you might be happier with a light tint of the color you like.
Small vs. Large
Small rooms can be a challenge. Window treatments, which control light and privacy without taking up a lot of space in the room, make sense in small rooms. Fitted interior shutters, shades, and café curtains tend to work well. Save voluminous fabric, elaborate swags, and draperies that “puddle” on the floor for large rooms with high ceilings. Furniture needs to be scaled to the size of the room, too, although one occasionally sees a small room with a few large pieces of furniture, which look dramatically good and serve the intended function well.
Summary
The biggest key is to know what you want before you start. Get that answer straight in your mind and you can’t go wrong.