Paintings. Peruse the internet for affordable paintings. Many artists have blogs and are struggling to support themselves with their art. Second hand stores often carry original work as well (see my post regarding a thrift store in Toledo, below). Or call your local art school to see when they are having a sale. It feels great to support local artists. Remember to go large. A large painting can be used to anchor each area of your apartment. Lots of little pictures grouped together looks cluttered.
Pillows. Etsy has lots of affordable pillows (see post below). Target also has a nice selection of pillows. I never buy pillows in second hand stores, it doesn't seem hygienic. Textiles add a luxurious feel to your place, but don't be lured into spending a lot of money. I have bought beautiful silk pillow covers from Thailand on Ebay, at extremely reasonable prices. The pillow insert can be bought at the craft store for a couple of dollars.
Lamps. Add an unexpected lamp. I suggest a standing lamp to start with until you decide what sort of tables you want. Also, standing lamps give a much more pleasing glow than overhead lighting. Second hand stores often carry cute lamps, but beware the lamp without a shade. It can end up being very costly. You can find a cute lamp for cheap, and rewiring is cheap. But lamp shades are hard to find in the correct size, and can be extremely expensive. One time I bought a lamp at a flea market for $2.00, the rewiring was $9.00 (total $11.00). I could not find the shade I wanted. I finally found one at a lamp shop for $55.00. I bought it because I was desperate and tired of the search. It was a gorgeous shade. But how silly. The shade was five times the cost of the lamp! Target has some nice lamps, as does CB2. CB2's lamps can get a little pricey, but they do go on sale.
You get the idea. A quick word about coffee tables. Forget traditional coffee tables. They are boring. Get creative. Use an ottoman, a trunk, a rolling cart, a tray, an outdoor table. I once saw a room with crappy wood crates, painted beautifully used as coffee tables.
I hope this has been helpful. Please contact me if you would like a consultation. I am available to consult on: where to start with your decorating strategy, using color, buying art, organizing and decluttering. Over the next several days I will explore how I use this formula in my own decorating and how I use color.