Improve your diet. Frequent bruising indicates that the body's clotting factors are not strong. Take more vitamin K. Vitamin D is another natural clotting factor. Some people are more prone than others to produce bruise spots. That can be a sign of kidney and liver disorders.
Anemia can also cause bruising, as well as allergies.
Leukemia can also cause frequent or large bruises. Aspirin causes internal bleeding, and can increase surface bruise marks. Alcohol and hard drugs will weaken the clotting factors also. Helpful herbs include burdock, aloe vera, cayenne, kelp, and white oak bark. Garlic, alfalfa, and rose hips are useful.