My husband and I have tried using bold colors in our decorations in an attempt to contrast the stark white walls. Our apartment is still a work in progress because we can only spend so much
so often, but one thing that really helped out was making curtains for our bedroom.
The apartment came equiped with blinds, so privacy was not an issue I had to deal with, although my solution would work to help out with that as well. My solution was to use bedsheets, but to be creative in my method of putting them up.
Because of the size of the windows, I chose twin sheets. To custom fit them to your window size (if you'll look closely, the two windows in our bedroom are two different sizes), you can simply make a "Z" shapped fold on each end of the sheet. It really is quite simple. You measure how much overhang you have on each side of the window after you center the sheet on the window. Then, take the sheet where you want it to end (the edge of your window or slightly past), and bring the edge of the sheet to meet that spot. After doing this, you should have a loop of extra sheet. (If you were to spread the layers apart slightly, it would make a "Z" shape.)
All you have left is to fasten it to the wall. I used push pins. Seriously. Since sheets are long, I
also had the ability to make a valance that hangs over the push pins to hide them. I did this
without cutting up the sheet, in case I ever wanted to use it on a bed again. I actually did this step first by measuring how close to the floor I wanted the edge to hang and having the excess just fall over in the front. (Of course, if you already have a rod on the window, the process is much simpler. Just flip the top of the sheet over the front of the rod and safety pin the two sides together.)
To make it more decorative, I took some ribbon I had lying aroung (never throw away ribbon, it has SO many uses!!) to tie around the middle of each sheet. And voila. No cost curtains.