Start by taking the measurements of the room, and use these to decide how big the piece of artwork you wish to install should be. For instance, if you want to put a painting above the sofa, then measure the space between the couch and the ceiling, and note down the measurements on a piece of paper. You will have to take these measurements with you when you go out to buy the artwork. You might even consider taking a photo of your living room with you - this can help you assess the artwork properly, before buying it.
Make sure you choose your art wisely, and check to see if it will complement the style of your living room. Any artwork that ends up looking odd and out of place will be a major blunder on your part, and no matter how much money you spend on it, you will most probably end up removing it one day. So, instead of wasting your money on something which does not go with your living room, try to put some thought into the selection process, before deciding on your final purchase. For instance, a simple watercolour painting will look better in a casual living room, as compared to an elaborate steel sculpture.
If your heart is set on a particular piece of art that does not fit in with the decor of your living room, and you feel that you need to have it at all costs, then you should rearrange your living room accordingly, in order to accommodate the artwork. Your objective should be to make sure the entire room is in harmony with the piece of art, and that there is enough space for the artwork to be properly exhibited.
You can also widen your search and look for diverse types of art, instead of focusing solely on photos and paintings. For instance, you can choose collages, sculptures or even an artistic mural. However, you will have to take extra care in order to blend these sort of prominent art pieces into the surroundings of your living room.
Before going out to buy art, you need to set a specific budget depending on how much you are prepared to spend. Rare and elaborate pieces of art will definitely cost you a lot more than regular artwork, so be clear on how much you are willing to shell out.