Cold compresses help the pain and swelling, as previous posters recommend. Be careful not to cause frost damage – use a layer or two of cloth or paper towel between frozen items and the skin, and limit application to 20 minutes.
But you can help the bruising resolve days faster with St. John's Wort (Hypericum) and /or Arnica Montana. These herbs are often available together in "trauma" oils, creams and gels at your health food store and at many chain drug stores. St. John's wort alone can resolve a small bruise before it becomes established, but even hours or days later, the bruise can clear out faster. (Apply around the eye, not in it.) Both these remedies are also available as homeopathic remedies that can help some people.
I was bopped hard in the eye by a young goat several years ago. By the time I made it into the house, my eye was swollen shut and turning amazing colors. I applied alternating St. John's wort and Arnica every 20 minutes, plus took the homeopathics. Four hours later there was NO sign of swelling or discoloration, only a small rip in the skin under my eyebrow and an abrasion skidding up to my hairline. I've had equally amazing results on smaller bruises using St. John's wort alone, but that's applying it right after the injury.
I strongly recommend these remedies for every mom's medicine chest! They're also good on sprains.