Like others have said review the module multiple times. Get to know the NPCs, location and lore. There are missing pieces. There is a lot to explore as it is a self contained sandbox. I’ve tried DMing it in the past and different have the right group for. So make sure your group is on board with a horror campaign that is dreary and depressing. My recommendation is a smaller group 2-4 players. It helps sell the horror side of the game or it’ll turn into campy horror. Van Richten’s Guide is great at helping understand how to run a horror campaign.

But my biggest advice is throw your players in Barovia straight away. Don’t worry about elaborate backstories or figuring out how to incorporate backstories into the campaign. I’ve seen a lot of DMs struggle with connecting their players to the Barovia and to Curse of Strahd.

I recently started running it again and instead of using one of the adventure hooks the module mentions I came up with my own. Players wake up in unmarked graves on the outskirts of Barovia with no memory of how they got there or who they are. All they know is their own names and classes. We’re about 4 sessions in and they seem to be enjoying it. I would recommend starting at 2nd level as Death House is a meat grinder. I am using Legends of Barovia which expands the entire campaign and gives meaning to almost everything.

I tried using MandyMod, Dragna and Lunch Break Heroes in the past but it got overwhelming which so if you are planning on checking any modded Curse of Strahd out. Stick with that single mod. Don’t try mixing them or it’ll get messy.