I thought I would start with something that a lot of us have trouble with in interior design - scale and proportion.
To be professional, we will need to make a fine distinction:
Proportion is the relationship of one part of an object, to its other parts.
In other words, proportion is the relationship of one part of a single piece of furniture to other parts of the same piece of furniture. For example, the cocktail table top below, that is in proportion to its legs.
OK, so now what?
Let’s assume that you found a sofa for a living room with suitable and pleasing proportions. Now you've got to visualise what will happen when you add different sized pieces to create a furniture grouping around this sofa.
Take the scale test. When you visualise end tables on either side of the sofa, you don't have to measure to see whether or not the scale works, you just feel instinctively that the scale is right. You will look at an object and instinctively measure it, not by its actual size, but by its visual weight.
The larger its shape, the heavier its visual weight. (OK that’s easy, what else?)
The more intense its colour, the heavier at its visual weight.
The bolder the pattern, the heavier at its visual weight.
These things we intrinsically realize, but sometimes we need to stop, look at our rooms, and see if we have design balance.
When you select furniture, you want to consider only pieces that are suitable in scale with one another. This is just another aspect of achieving harmony. A room cannot be harmonious if one or more pieces of furniture are out of scale.
Scale in large rooms. Big rooms can handle big furniture. In fact big rooms require big furniture. In addition, a large room can handle furniture that features intense colour and bold patterns. What's more, a big room calls for large architectural features too. Such a room seems more in scale if it features big windows, big doors and a big fireplace. In other words, the architectural elements of the room should be in scale to the size of the room.
Small rooms: Well this is where we break the rules, in the 'old days', we used small furniture in small rooms. But not anymore. We're finding that we can indeed use large furniture in small rooms - however the proportion of the furniture must be in proportion to the other furniture in the room. No large sofas and tiny coffee tables here!
In reality, these are not a sequence of steps, but rather common sense using the rules of scale and proportion.
Good luck and happy designing!