That's gonna leave a bruise!! You can't prevent them as long as you are active, but there are some things you can do to make an ugly bruise go away quicker.
Bruises are simply a result of bleeding under the skin, and fading a bruise involves making that pooled blood go away as fast as possible.
Ice it! When the blood vessels around the bumped area are cold, blood is less likely to spread out. Use a commercial ice pack in the freezer if you have one, or a bag of frozen veggies wrapped up in a towel. Keep it on for about 10 minutes, then keep it off for 20 minutes, and reapply it for 10 more minutes. Do this for as long as you can, until 24 hours has passed.
Wrap it! If you've bruised something that can be wrapped, like a leg or arm, wrap an elastic bandage around it immediately. Squeezing the vessels will discourage the blood from spreading.
Prop it! If you've bruised something that can be raised above heart level, doing this will discourage blood from rushing to the injury.
Heat it! About 24 hours after the injury, put an electric heating pad or hot water bottle on the injury for about 20 minutes at a time. This will help scatter the pooled blood.
Add vinegar to it! Now mix some vinegar with warm water and rub it on the bruise. Vinegar will help increase blood flow, which should chase off the old pooled blood. Witch Hazel is also good for this.
If you are willing to take the steps, your bruise will be minimized and the color will fade much quicker. Now if someone would just write an article on how to not be such a klutz!