The living room is actually a fairly new invention. The room which it supplants as far as popularity is concerned is the parlour, that comes from the French verb "parler" which means "to speak." The first living rooms were formal, like the parlour, but in the 1920s, the living room became a "place for families to play together." By the 1940s, the living room became not only less formal, but actually comfortable. When decorating the living room, there are some details to keep in mind.
The living room is, but one room in a house. So, the home design should influence the style of the living room. If the house is traditional, then the living room should be traditional as well. If the house is Victorian, then the living room should reflect Victorian influences. You don't want to create a room that looks out of place with the rest of the house, but which rather compliments it. Home magazines will reflect this when you look through them for home ideas. You do not have to be completely faithful to the period of the house, but enough so that it ties in with the whole.
The furniture should tie in with the rest of the house as well. However, there are a few considerations that are important. The first is the house's inhabitants. If you have young children, you will want to pick out furniture that you would not mind your children climbing on. The point of a living room is to create a space where everyone can be comfortable. You don't want to pick out furniture that looks wonderful, but which you don't want people to use because you're afraid that it'll get damaged. Materials that sustain to abuse, but which look beautiful are tapestries, leather, or any tightly-woven fabric.
Pick out colours that will tie in with the rest of the décor, as well as compliment it with area rugs, curtains, throw pillows and blankets. If you are interested in period colours, books and the Internet can help you to find that information. However, if you do not like the palette of the period, you can adapt it to suit the modern day in which you live. Hint at the period of the house without deviating too far from it.