[@Jangel13] You have a lot of options. Just gotta be creative.
1) Push a human in an alleyway...drink their blood...leave no evidence.
2) Lure a human into a secluded area, misleading them for sex, drink their blood, leave no evidence.
3) Steal packaged blood in the medical building xD. Leave no evidence. 
4) Find animals. Drink their blood. Doesn't matter if you leave a dead animal lying somewhere, I doubt anyone would care xD. Unless you rip open the animal. That would be suspicious.