set your budget
Decorating can be done extravagantly or minimally. The main factor that determines your place on that spectrum is your willingness to spend. Figure out how much you have to spend on furniture, carpets, decor pieces like mirrors, etc. If you are on the low end, check out these DIY decorating tips.
If you have a bit of cash to spend, look into an interior designer. Sometimes, they can pay off in the long run, in terms of value added to a house.