Your bedroom should be your space. Choose wall art that you love and that excite and/or inspire you. That will be soft colors for some, bright colors for others. The general rule of thumb is, however, that bedroom decor should promote relaxation, so using disturbing wall accents that may negatively impact your subconscious mind or glaring colors that may stir your emotions is advised against.
Over the bed is the usual spot for wall accents, such as a large painting in "your" colors of a meaningful subject or an abstract that enthralls you. Make sure the painting is not wider than the bed and is roughly one-quarter of the distance between the highest part of the headboard and the ceiling.
You may also want to highlight another item of furniture, perhaps a dresser or nightstand. Place an eye-catching wall accent over it, such as a resin sculpture finished in faux bronze that represents the intertwining of hearts, bodies and minds.