First of all, "ART" is in quotes in the title of this post solely because I'm broadly defining it to mean any sort of framed wall decor (poster, hand-me-down, needlepoint, etc.) that you have, or may consider having, on your wall. It's NOT a snide way of indicating that these items aren't "real" art; I'm not elitist about the fine art world at ALL and my goal is always to help people spend wisely and to make their walls awesome.
That said, art that you have already quite possibly isn't living its best life right now; there are often ways to make it look better. Here are a few: