The framing on a painting can dramatically effect the appearence. There are some standard frame guidelines and books and web sites that will give you advise. My opinion – it is great to have a period frame on a work. Like most rules there are some grand exceptions. A modern print can be stunning in an antique frame. Wider can add importance and grandeur but wider is not always better. Personal taste counts. If your decor is Mission Arts & Crafts a wide ornate gold frame is going to look out of place. If you purchase a painting in its original frame and decide to replace it its a good idea to save the original frame. Collectors can be particular about original frames and it will help preserve its value if you ever sell it to have the original one. Its best to be able to try different styles on a work and let your eye tell you which combination is the most pleasing – sometimes this is a surprise and not what you were anticipating would be the best. If you are going with a contemporary frame let a professional framer try their different corners on the work and pick the one you like the best.