Lets start with the three basic Guidelines of what makes a room successful:
1. Function – something is useful, conducive.

2. Mood – feeling, expressive of some form.

3. Harmony – agreement, the fitting together of parts.

Long before you get to worry about colors and fabrics come the
basic rules of design:

1. Function

This one is obvious but you rarely think about it alone. Every room has a particular function. The kitchen for cooking, the Dining area for eating, and so on. Have you ever thought about additional or secondary functions, say a kitchen may also be a space where you run a small office, therefore you would need special planning to make sure these activities can be done here. As you see there can be more than one function to every room. What about the living room? T.V., Entertaining, Reading… is there light for reading? Tables for drinks? A TV? Seating for entertaining? The list can get pretty long. As you can imagine you would need to know what the intended use of each space will be, so that every function can be served. So you must know in advance to decorating a room what function it will serve. This is what will set your decorating apart from the inexperienced decorator. So you must always know what the room will be used for.

2. Mood

Every truly successful room will have a particular mood being expressed. This is done by giving it a feel, this goes hand in hand with the style you choose for a space.

Examples:

A room you will be decorating is in a high-rise. You want a modern feel. You then decide that the mood will be of sleek modernism. Straight lines, cool, and contemporary. Another room you decorate may be in the desert far off from modern conveniences, built with an earthy feel, an adobe home, you may love earthy tones. You would obviously avoid the mood you created in sleek apartment. Instead you look at the architecture of the home. What type of furnishings are in the other parts of the home? What mood should it express? You decide on simple southwestern theme. You would use simple American styles, with Indian style fabrics and natural casual feel. Warm, inviting, cozy, and simple. Warm colors such as yellow and red with turquoise accents.

I am sure you are getting the idea of Mood at this point. Look in your favorite magazines and note the colors, furnishings and textiles, see how the room will have a mood, a style and a feeling of Harmony.

3. Harmony

The Golden Rule of Interior Design is: Harmony
Think about it – this basic concept is the foundation for every room. With out Harmony a room will not “work” or fit together.

So what is Harmony?

It is a pleasing or congruent arrangement of parts. The whole objective in designing a room is that everything in the room fits, it must all work together to complete a space that is pleasing.

Now you are thinking to yourself, okay that’s great but what do I do with Harmony?

Simple, you always remember, you must have balance to every space you decorate. Every space will have it’s own feel to it. You must decide on the mood you want a room to express. How do you want the space to feel? The reason you must do this is because different moods reflect different colors and styles of furniture. This will be very important. You would not want to select a modern piece, with harsh straight lines, for a room which has a simple country mood. Neither would a simple wooden rocker fit in a sleek modern apartment. This is where harmony comes in. Can you imagine a king sized bed in a small studio apartment? No it would be terrible the bed would not be in scale to the rest of the room. Yet it would look wonderful in a very large home. So make sure that everything selected to go into a space is harmonious in size as well. You have just learned a basic rule. Every space must be harmonious in feel, style, and size.

Harmony is actually relative to furniture selection more than any other thing. Why is this? An empty space itself has nothing to harmonize with; it is when you add furnishings to it that this rule applies. All furnishings, colors, window treatments and so on must be harmonious in STYLE, FEEL and SIZE. Remember the king size bed in the studio apartment? This is an example of SIZE Harmony. What about feel? This really means the mood and style you have selected for the space. In order for a space to be successful it must maintain a feel or mood suitable to the style.

When you see a room in Better Homes and Gardens, it looks right, everything in the room seems perfect, just right. It all “works”. I mean that everything in a room comes together, it all goes, colors, styles, fabrics and so on. Your eyes can flow through the room with ease. There seems to be a focus and a good blend. So keep the ultimate object in mind: Harmony.

Harmony is actually very simple. Everything should be harmonious in mood, scale, quality and color.

To wrap it up, these are the key points which you must remember. When you select a color, a piece of furniture, or fabric, you must ask yourself if they are in harmony with the design you have planned.