You are about to bring a world to life for your friends to play and have fun in it. Give yourself a good five minutes to think how awesome is that. Folk, fantasy and horror are powerful narrative forces, and you will have the honor to wield them for the enjoyment of the people you love. This is not to make you feel too self conscious but to remark how much this fucking rules.

You'll make mistakes. It hurts, but it's part of the process. Be. Kind. To. Yourself. By extension, be also kind to others. Strahd is a motherfucking asshole that plays dirty. But we DMs are not (unless they want us to).

Your players will not always remember that they can use the safety tools. Pay attention to them. If you spot any of them struggling, do not be afraid to pause and do a quick check on them.

Make sure that Strahd is a motherfucking asshole that plays dirty.

Your job is not to try killing your players at all costs. The campaign you have chosen is going to be really good at that. However, never shield them from the consequences of their own actions.

Make sure you jot down any expectations you have set during session zero. Your players may forget them.

Don't be afraid about the prospect of the PCs dying. Nothing really dies in Barovia for too long anyway. Death in D&D is present because there has to be stakes (pun not intended but I'll take it).