The way you decorate a room is always going to have a big impact on the way it ends up looking and on the way you end up using it. Of course your interior design is very important for the appearance of a room, and this is the main reason that many of us will take time arranging our furniture and fittings (other than the fact that we are excited to decorate a new room or home) . But what you also must remember is the way that the room layout affects your day to day use of it, and even the way you feel when you're in it.
Making a room light and spacious for instance is something highly worthwhile and certainly worthy of some time and thought. If your room is small, cluttered and dark, then this can make it difficult for us to relax as we feel 'hemmed in'. This is particularly true for those of us who suffer with claustrophobia and other similar conditions. At the same time being in a room that looks dark and cluttered is always going to feel smaller and we will not want to spend as much time relaxing in it as a result. And lastly if it actually does have less space then this affects what we are able to do in it.
So the first way to ensure that your interior design makes the room spacious is to actually ensure that you don't clutter the room up too much. Remember that often in life, and particularly in interior decorating, less is more and if you have too any items vying for attention in your rooms then this will only serve to dilute the impact of each one of them. If there are so many loud objects, paintings and items of furniture that you don't know where to look, then people won't be able to appreciate the quality of the items on display. Instead feature just a few items in your interior decorating and you will find that people are drawn to them and they become center pieces.
Aim to create as many empty spaces in the room as possible. This means not only avoiding physical objects, but also anything that breaks up a plain space. For instance a rug is great for a room that you want to look 'cozy', but if you are trying to make a room seem bigger and lighter then actually a rug can just end up registering as clutter. Likewise too many pictures on the wall, or too many items on a table can also make the room appear smaller due to lack of visible 'space'.
Recognize also that light translates as space. One way to make a room look bigger instantly then is to use lighter colors on the walls and floors, and to let more light in through large windows. If your interior design is able to involve actually knocking through walls etc, then consider going for a more open plan design which will ensure that everything seems larger and more integrated.