Fresh blood is an easy stain to get out. The key is to keep the stain wet, rinse out under the tap in cold water. If you have successfully rinsed the stain just launder as usual in cold water.
If the stain is old soak in cool salt water for a long time (hours) and rinse thoroughly. Soak again in water with a some ammonia. Launder as above. Since blood is organic you can try soaking in an enzyme solution for half an hour to an hour. As a last resort bleach if the clothes are white, or use a color safe bleach. Heat will set this stain.
Always test a small area with any solution you are going to use on the clothes to test for color fastness and damage etc.