There are a number of ways to make a smaller room feel a bit larger then it is and the first thing you should consider is the best way to utilize every portion to its fullest.
When purchasing furniture for the room you should buy size appropriate furniture and not try to fit larger pieces in the room. If you are decorating a bedroom you will need to use the smallest bed that you can comfortably fit in. This will probably mean choosing a Double or Queen sized bed over a King Sized bed if two people will be staying in the room or a Twin or Single over a double or larger sized bed if only one person is using the room.
Some people may consider a fold out bed but they are not a reasonable solution for extended periods of time and they can also be uncomfortable.
If you will be purchasing a couch or chair for the room you should consider a bench that will allow seating but also provide storage. A single chair can provide seating at a desk for studding or other reasons but it should be able to fit under the desk to allow passage. If this is a child’s or teens room the bed can act as additional seating.
Light colored walls is the best idea and the same goes for carpets and window shades and drapes. A combination of a thinner drape with an aluminum, wood or other solid blind can block most of the sun even in the day time and allow privacy while still letting you increase the light in the room by opening the blind and keeping the drapes closed.
A single light on the ceiling will be mandatory for building code but you may want to increase its function by adding a low profile ceiling fan that can fit close to the ceiling but still provide good air circulation. Discount fans can be found for about or under $50 when on sale.
A decorative bed spread can bring some interest to the room. You may want to find bed linen that matches your interests or simply find a nice quilted pattern. You can also make your own quilts with remnant scraps available for next to nothing at a local fabric store or made from old clothing and other cloth items. For the core of the bed spread you could select a cheap comforter that will allow you to assemble the piece with a sewing machine or you can buy the same material in rolls at your fabric store.
When selecting shelving it is better to reduce the depth of the shelves and extend them to the ceiling of the room. Make sure you take full advantage of space that would normally go unused in other rooms.
TVs can be mounted from the ceiling or a wall if you use the proper mounts and place your anchor screws into the studs or ceiling joists.
Finally you will have to decide what items you want to store in your room. This means being selective when deciding to keep things you don’t use or need for long periods of time. If you have something that you haven’t used in 6 months put it on the get rid of list. If it is still there in a year then you really need to get rid of it unless it is sentimental. Cardboard boxes full of old shoes or clothes that no longer fit are not sentimental but if the item has worth then sell it on Ebay and put the money in the bank or donate it to charity and take a tax write off.