Drapes can hide a small window or minimize a large window. The look you end up with is up to you. Furniture is the next biggest expense. Re-upholstery is not hard, but can be time consuming. Pick a color that suits your lifestyle.
Slipcovers can be attractive and are usually less expensive than new furniture and re-upholstry.
They are also easier to clean. Rugs are nice, as is carpeting. Again, watch the colors to make sure they match your drapes and furniture. Don't be afraid to put an attractive throw rug on your carpeting, unless of course you have someone who uses a cane, or wheelchair. Carpeting helps to deaden sounds and can be formal or informal depending upon the color, pattern and style.