If you had plenty of money, perhaps you would want to actually open up the room or put a window in, but mirrors can help if you can’t afford an expensive remodeling project. Framed mirrors can even look like windows. Place artistic items in front of mirrors to show them off. Mirrors can also be hung in patterns on the wall. If you love the idea of mirrors, you could even buy all sorts and sizes of mirrors at a used store or off of craigslist or ebay and then display them all on one wall pieced together about an inch apart mosaic style.
Cover up imperfections that you would otherwise have to pay to fix. This probably isn’t something you want to do permanently, but if you are struggling financially it is a way you could keep your home looking nice temporarily. If your floor has a stain you can put a rug over it or even rearrange your furniture to get by until you can afford to replace the flooring. If your wall has a dent or hole cover that spot with a tapestry or picture until you can fix the wall properly.