Emphasising horror in Vampire.
Most of my suggestions are classics, but this one came up while I was typing:
Another idea would be to start every session with a short recap of what happened previously - but instead of framing it as a neutral "previously on..." sequence, emphasise all the horrific things that happened, especially the ones the players' characters did. You could also bring this into the ongoing chronicle plot, with a pair of homicide detectives investigating crimes that the players know the Kindred - possibly including their own characters - were involved in. It might keep the players on their toes and careful about the Masquerade, and also remind them of what happened in the previous sessions, as well as showing the mortal view of what they and their contemporaries did.
So I've now added that to the section on mortals for my next possible Vampire game.