When you add artwork to your decor, it adds more than just a finishing touch, it is a reflection of your personality and style. Artwork can resolve design dilemmas, particularly those where the perception of space can be changed by the art that is used. I've addressed some of the most oft asked questions for using art here.
1) Does my art have to match the colors of my room? Not at all. If you have multiple pieces to hang, it's preferable to select the ones that most complement the decor. Keep in mind that a bold contemporary piece will work in a traditional room, as will a plein air painting in a modern space. When you are custom framing a piece for a particular room, select mat colors that complement the colors in the art and the space in which it hangs.
A piece hung low to balance the chest and accessories.
2) How high should I hang my art? This largely depends upon the scale of the piece, the wall height, and what is nearby. For example, a 14 foot wall may require a large piece, but hanging it at what is considered "eye level" may be too low. If you are under 5' tall and your family is over 6' then clearly "eye-level" differs. A general rule is to hang art so the CENTER of the art is 60-65" from the floor. This measurement is also relative to the nearby furniture and architectural elements - a sofa, a table, a stairwell. Do what appears pleasing rather than be limited by an actual measurement.
3) What size art hangs where? The scale of the wall where you will hang art is important. A narrow wall area is best with smaller art, that fits that scale, whereas a larger wall area is best balanced with larger art or a grouping of pieces. Be sure to relate the size of your art to the furniture around it. The best balance is for pieces to be smaller, not larger, than the furniture.
4) Is one direction better than another for hanging art? In general, if you are hanging art over a horizontal piece, hanging the art the same direction tends to work best. Horizontal lines visually expand a space. In hallways, vertical lines help elongate the floor-to-ceiling line, often making the hallway look more expansive. All pieces hanging the same direction in the same space may be too repetitive so don't line your living room with only horizontal pieces, break up the direction by hanging some groupings or use the vertical plane.
Symmetric art hanging. Balanced by architectural moldings.
5) Symmetry or not? When art is hung in symmetrical arrangements flanking fireplaces, sconces, etc...it is more traditional in feel. Asymmetry is considered more casual and definitely eye-catching.
If you relate the scale of your art to the scale of the room, and hang it in relation to the furniture or architectural details nearby, you will have a great deal of flexibility. Have fun!