In this situation, if you're using your own blood, you have to be very careful and always use sterilized equipment.
Let's say you have a little offering bowl for Hades with his favorite things in it. You can simply prick your finger and let the blood drip into the bowl. You won't need much and you shouldn't use alot. You blood is your life essence.
I wouldn't call it much a sacrifice. More like an offering.
What some people do is prick themselves with a sterile lancet and smear blood on a symbol of the entity they want to commune with. This establishes a spiritual connection of sorts and is not necessary as a routine sacrifice.