
COLD water on blood stains, nevereverever hot water, it 'cooks' the blood in and then you really wont shift the mark.
I got a LOT of blood (mine) out of Mothers off white sofa cushions, just by soaking and rinsing repeatedly in cold water. Carpet is harder as it to really rinse it out you need to soak it and then it goes into the underlay. If you can, lift the carpet and get something underneath so you are washing it through, out to whatevers underneath (old towels) then thats much better but obviously its not always possible to do.
Once you have rinsed and rinsed and rinsed, pat dry as best you can (old towel and then jump up and down on it), then bicarb of soda, or salt.. dump that on and cover with a towel and leave it to dry then vacuum off, that should pull the rest out.