Prior to this photo I spent 5 minutes quickly drawing up a sketch of a tree overhanging a stream. Couldn't be bothered including it as it has nothing to actually do with the bleeding.
Just before you start working, have a pencil sketch of the piece you're going to work with on hand, once you've got the blood flowing it's kind of impractical to be moving around.
Got here a knife (just a good pocket knife, stanley knives, kitchen knives, razor blades, whatever will do. Just as long as it's sharp, but not too sharp so that if you slip you're not killing yourself, powersaws and scalpels are a no!), fine brushes (quite small), a jar of water (remember to always have fresh water!!! This is a health issue! Use a clean jar as well. As you can see I couldn't be bothered finding one. If you can't find a clean jar, use a clean cup. Keep this one JUST for your blood art) and tissues to keep the mess down.