A bruise results when a part of the body is exposed to extreme pressure. What happens is that blood pools just beneath the skin. These pools of blood are what you actually see as blue or black patches - your bruise. Bruises disappear on their own, most of the time. Naturally, you would want your skin to appear normal as fast as possible, so there are things that you can do to quicken the healing process. Needless to say, you will still certainly have to put up with the bruise for at least a couple of days.
The first thing that you need to do is to immediately deal with the affected area even before a bruise starts to form. Apply an ice pack to the area for five to 10 minutes to stop the blood flow and keep the swelling down. You may use commercially available ice packs, or if you do not have any of those, get a pack of frozen vegetables or ice cubes. You can wrap these in tea towels to make it more comfortable for you. You can repeat the process several times if necessary.
Also, try to keep the affected area higher than the heart if possible. This will make it difficult for the blood to flow into the bruise, which will actually help in avoiding more blood from gathering in the area.
Now, you may be tempted to take pain relievers. While it is not such a bad idea, especially if the pain is bothering you greatly, you ought to make sure that the pain killer that you get does not promote blood thinning. What you need is to stop the blood from pooling in the bruised area, and if the blood will not clot, you will end up with a more serious bruise.
Lastly, you may use some herbal creams and ointment that are supposed to help make bruises disappear more quickly. While they may not have much scientific evidence to back them up, using witch hazel or glycerin will certainly not do any damage.