Unless you have some kind of periodontal disease, you can do some rinsing. Take a big mouthful of water and hold it for about 30 seconds making sure the water inside your mouth covers the area where you are bleeding. Then spit the water out. Repeat this several time until the bleeding stops. If it doesn't you need to see a dentist.
You should also get as much Vitamin C as possible. Drink a lot of orange juice. A long time ago, sailors and pirates used to get scurvy (bloody gums) because they had no source of Vitamin C when they were at sea.