It isn't clear if you are talking about making it look bigger from the outside or from the inside.
From the outside you can try to remove trees and brush from around the house that makes it look like it is being closed in on.
There are many more things you can do on the inside to make it look bigger.
Using light colored paints on the walls will make rooms feel more open and larger than they actually are. Also removing clutter from the room will make it appear bigger. If you have too much furniture for the size of the room it is going to feel very cramped and smaller than it actually is.
As others have mentioned, lighting is equally as important. This ties in to the paint color as well. A dark room is just going to seem much smaller than it actually is. Adding as much natural light as possible will make a room feel more open and inviting.
Finally, this is a personal experience. If you are able to removing the attic and having vaulted ceilings installed will make a huge difference in how the space feels. The last two houses that my wife and I have lived in had vaulted ceilings and it was amazing just how much bigger it make the rooms seem.
Something about the wall and the vertical space carrying all the way up to the peak of the room draws your eyes and makes the house seem much bigger than it really is.