I love this page, it's very very helpful. I've favourited it, and I think I'll print it out as well. You never know when you'll need this.
I try to work clean, and most of the time I achieve this, but on my last piece of cross stitch, (luckily dark blue linen) I somehow managed to smear a purple cough sweet onto the fabric. Uggh. I let it dry out, and then prized it off. Then I wet the area a little, and it's seemed to be ok.
My nurse friends tell me that with blood, like from a pricked finger, always cold water, never hot. And some of my older friends say suck a piece of floss and dab at the blood stain, though I've never tried this out for myself.