Firstly, you need to choose the colour palette you want to work with. Calming colours are always a good choice such as pastels and neutrals. Choosing these colours will also make it easy to match furniture and other elements together in the room. Remember, simple is always best.
A vital element when decorating your living room with a contemporary theme is your wall treatments. For this design style the colors can make or break the look - consider adding shades of browns and black or a sharp black and white look to the room. Try using a neutral color paint on the walls, or if you want something different go with a leather or suede wall covering.
This is not to say that all items need to be made in the same period, have the same texture or be of the same color, but instead that you should stick with a few themes and make sure that one or two are reflected in each and every piece of furniture that you have in your living room.