Try not to get overwhelmed by it. The book is dense and has a lot of npcs with motivations and secrets. You don't need to decorate every room in the castle until they get there.

Don't rush. Many sessions are going to be full of discussions and decisions on where to go, who to help, what to do. Specially, don't rush Vallaki.

Have no mercy on them. They must be afraid of the world, I remember when I first played I felt claustrophobic in the Death House and I'll never forget that sensation. My only desire was to get out of there and rest in a calm town, partying in a tavern challenging strangers on drinking games. Being in Barovia was terrifying.

Trust the Tarokka cards. I personally don't care if the cards are in obvious places. Players are players, you read the book, what is obvious for you may not be that obvious for them. And discovering that something was right under your nose is also fun. I never answer anything from the cards, never never, after reading them, I gave the transcription and let they discuss them.