living room curtains will be heavily influenced by your family's lifestyle, and how you use your living room.
Quite often the living room is one of the largest rooms in the home, and has large windows to match. A large window give you the chance to use the welcoming effect of fabric to full advantage. You can achieve both a luxurious and cozy effect simultaneously. It's also the room which may be in constant use, during the day and especially in the evening.
So one of your aims may be to allow as much light in during the day, while in the evening to have a room with a certain amount of impact.