...are people who drink blood, not only because they feel attracted to it (see Blood fetish) but also they feel a physical craving to have it. What's the reason behind this I couldn't yet discover, but what I can say from my personal experiences is that withdrawal can cause very similar effects to those of "hard drugs" like Heroin or Alcohol. There is no denial: it is an addiction! The effects range from physical effects to depression. Some vampires develop substitute addictions who can range from chocolate to more serious drugs. Many Sanguinarians suffer from various forms of eating disorders. (Oh yes, even Sanguinarians need other food!)
Well, there is a silver lining: The craving for blood decreases with time! Probably this is caused by an increase in mental power, another theory is that this is caused by a better developed ability to substitute blood through other sources of energy (see Psi-Vampirism).
But what if you are a young vampire and not yet able to control yourself? Well, you better learn soon or you'll be in trouble! Always be aware of the fact that you as a HUMAN being have a responsibility against the people around you. Few vampires attack people or want to harm them. Aggression is always a sign of personal weakness; even a vampire has to work on this. But what to do?
A few words of importance!! Drinking blood -both human and animal- is always a very risky endeavour. The risk of an infection is very high and should always be considered. (Remember: (most) vampires are not invulnerable!).
But where to get the stuff?? The least problematic possibility is to go to your local butcher, who will sell you animal blood in larger amounts at low cost. (Never mention you want to drink it). Good excuses are "That's for a special school/university project." or "I need it for a special Scottish/Bulgarian/Caucasian recipe". However animal blood can never be a full substitute to human blood, since the latter contains far more energy (my personal view).
Getting human blood is much more difficult. Finding an reliable donor is a task which should not be underestimated (both out of medical reasons and personal trust). An US development is to form a kind of "feeding circle" where the few readily available donors are shared. But even if you find someone willing to give his blood you should always check his/her motives to do so. If one discovers a weakness in the donor who makes it impossible for him to resist one's wish one should evaluate the harm the feeding could have on this person. The only rule I personally follow is to respect the source of life I take from.
There still are many people out there who have other motives. Most of them are teens in their "Vampires are cool!"-period, who usually want either a romantic experience or plainly want to be turned (a thing which - in my view - is impossible; See latent vampisim). No doubt exploring this willing sources is a NO!! Though some donors might find sexual pleasures in the act of giving, it always includes some pain. The actual bloodletting can best be achieved through a cut with a (clean!) razor-blade. The wound heals quickly and usually few scars appear. (I will not tell you any place to use, as this practice is always dangerous, so this is up to you to find out.)
However, the consumption of blood is always a pleasure - satisfying, on a physical as well as on a personal base. It is the act of sharing life, a very intimate experience between two people, comparable to nothing!