The best way to lighten a bruise is to apply a cold press immediately after injury. This reduces swelling, slows blood flow and keeps blood from pooling under the skin.
Using a cold press for 10 minutes, resting for 15 and repeating for the first three hours after injury helps keep bruising to a minimum. If a bruise does appear, it will likely be much lighter than if a cold press treatment was not used. Wonderhowto.com also suggests that a mixture of Cayenne pepper and Vaseline can help reduce the pain and visibility of any subsequent bruising when applied directly to the skin.