For blood (and especially old dried blood), I’ve found that oxiclean in cold water works well. Fill a bucket with a small amount of the hottest water you can and put some oxiclean in. Give it 30 seconds to dissolve, then fill the bucket up with cold water (follow the instructions for quantities of oxiclean and water). Then, put your bloody garment(s) into the cold water and let them sit for about 6 hours. Remove from the water, gently press some water out, and immediately launder your clothing as you normally would. If there’s still blood, do another cycle before washing.

Don’t do this if the care tag specifically excluded any form of bleach. In my experience, it works especially well on period stains.