Clean, clean, clean. Even if you have the largest room ever, if you have things that you don't even use, there will be clutter as a result. Either spend a whole day of getting rid of stuff you don't use or need, or do it gradually by donating or selling things, as well as throwing things away.
Use a light neutral paint color. Light colors "open up" a room and give the illusion of a large space. My personal favorite is a very light gray that is almost white. It gives you a great template for adding different patterned furniture and accessories.

Mirror, mirror on the wall. Adding mirrors around the room will reflect the room and it will make the room appear larger, similarly to the paint.

Take advantage of any windows. Natural light is the best way to enlarge a room. Utilize drapes in a manner that will make the window appear larger.

Use space-saving furniture. In my room, I have a folding desk that is mounted on the wall and I can open like a chest to a desk. Another space-saving piece of furniture would be a loft bed for rooms with high ceilings. This way, you can use the space beneath the bed as a desk area.

No room is perfect, you gotta work with it. You just thought of Hannah Montana, didn't you? It's okay, so did I. Instead of placing your furniture and whatnot perfectly against the wall or in a straight-in-line manner, try placing them at angles that you may think are awkward, but it will actually make your room cozier and less claustrophobic.

I hope you try out these techniques because they have all worked for me. :) If you want to check out the original post, click here. Some of the ideas I took from the website, and others were simply from my brain. :)
Works Cited
Bourne, Leah. "How to Make a Smaller Room Look Bigger: 25 Tips That Work".
Stylecaster. 14 Mar. 2014. Web. 3 Dec. 2014.
Stylecaster. 14 Mar. 2014. Web. 3 Dec. 2014.