Sacrifice is a common practice in demon worship. We sacrifice blood or other parts of the body, food, animals (also as food), oleums, scents, energy, objects, etc. But what is interesting and crucial here is that Demonolatry stress understanding of term sacrifice as “to make something sacred”.
Because of observed limited resources (physical resources, money, time), in western culture we are used to think that it is necessary to give away on something to gain something else. In result term ‘sacrifice’ is mostly understood as ‘to give away something to gain in advance something else”. We are taught “no pain, no gain”. However Demonolatry try to focus more on abundance then rather lack of it, what transforms the whole approach and its symbolical meaning. The act of sacrifice may look similarly or the same but the reason for it is completely different.
Making something sacred implies symbolical rising of the value of scarified object. Not to gain something but mainly to appreciate what we have and to thank our deity. We may receive something in return but that is not the main cause only possible byproduct. It also symbolically shows that we have something in abundance (it doesn’t have to be true, but we should approach it that way, gratitude should be honest) and we can share it with our deity. In other words, scarified object focuses on gratitude and abundance and make law of attraction works for us.
If you’re going to kill for a sacrifice, then sacrifice should be sacred, meaning it must be treated with best regard and should be killed as humanely as possible. Not because it’s right or moral but because you owe it to the sacrificed “object” (it contributes to your well being!) and because in the ritual you thank for all it gives you. Sacrifice is physical manifestation and powerful symbol of it and richness always comes from and is manifested by gratitude. I repeat it once again: you sacrifice a piece of abundance to gods/demons to thank for it, so sacrifice is actually an appreciation ritual.
In earlier times killing of animals was a blessing, because animals provided us with all needed and good things, so it was natural to want to please or thank gods with what people found as essential to survival. Nowadays, we don’t depend so strongly on hunting or breeding of animals. The source of our abundance are shops, work, money so sacrifice involving killing is anachronism from past times. Still you can either use this old symbolic and do it right or rewrite it to more proper way in present situation. It is your choice.
A bit different symbolism may be carried by self sacrifice (blood, parts of the body). However in no point of sacrifice we need to feel pain or resign of something (self mutilation is not a part or goal of Demonolatry!). In general, symbolically piece of yourself is moved, transformed toward deity or essential element of the deity. So self sacrifice means to share of your unique essence, to make a bond, toward self deification and unity with chosen demon.
Notice, that sacrificing of blood in details itself is another topic because of reach symbolical meaning of blood.
In theistic satanism sacrifice is practiced rarely, although many think of it as crucial practice of satanism. Most theistic satanists (or satanists in general) don’t feel obligated to any special devotional rites, hence sacrifice is often used in distorted way by dabblers, who take christian propaganda as truth instead thinking for themselves. Of course it’s not always the case and some satanists do know what they’re doing and practice proper sacrifices.