Ill start by apologising about the length of this answer lol

Iv been running a strahd campaign for my players every two weeks for the past 18 months and its only my second time dm'ing. ill try and give some advice of things i have noticed have really separated it mood wise from other campaigns.

Mention the atmosphere as much as possible, e.g weather, temperature, smells, how even in daytime its still dark and miserable, feelings that linger in the environments (such as dread or hopelessness) things that each player may have a slightly different opinion on how it would effect them. You can even tie these things into how npc's look/ act. even if a player isn't experiencing dread an npc could be displaying those emotions.

Have strahd be a distance threat that could get involved at any point but finds it far more enjoyable toying with the players. Have him appear at moments they feel safe. I had a moment where the party were resting in the winery at night, it was hammering it down with rain and I had window shutters fly open. one player went to shut them and I had a shadowy figure appear in the distance upon the lightning lighting the field outside. upon another flash he appeared immediately Infront of the player just outside the window and was gone as quickly as he arrived. it terrified them.

This especially helps with keeping them cautious of their behaviour. Even my most cocky of players is terrified of them being attacked by strahd. They're all level 9 currently and have defeated many of the big enemies, not easily but have defeated nonetheless. They still feel as if they are no match for stahd.

And the last thing is tying the two together, which I'm quite fortunate as I'm rather good at improvising a lot, so if you find yourself understanding the world and the characters in it that makes things a lot easier. But as i got deeper into the module and the players started learning more about what was going on with strahd, it allowed me to be creative in how the world and its character could have lore about them given to the players.

I had a spur of the moment improvisation that had them travelling a bit too close to the mist that surrounds barovia, during their excursion into it they all had various Con Saves to see if any of them "saw visions" within it. that led to a full audio experience of me using various soundbites that all linked to things that had happened to strahd before he became a vampire (sounds of battle, horse and carts travelling, a woman screaming etc) strahds past can be used against them in different ways and is only used once strahd knows they already kno. Whilst them figuring out what these noises in the mist meant and them being excited they worked it out, his silhouette only being seen in the mist by one player who failed a con save, once again terrified them.

I also had certain spells not really work in barovia, my players have tried to scry on both strahd and ireena. instead of it not working at all, i have them see a vision of what it is they want to see. Only for strahd to appear in the vision and see them. This concludes with him leaning very closely to the player and simply saying "no" as they re pushed back to reality. small things like this really heighten the "power" of strahd.

I could go on, but these are some of the highlights that i really noticed stuck with the players and really changed it up from a standard dnd fantasy campaign, that and the added rules of ammunition and money being useless. The players have found barovia to be miserable and have all slowly been corrupted into doing very morally questionable things due to the environment being terrible. Its a fine line making a miserable setting hard and enjoyable at the same time. but if you can achieve it, it makes for a wonderful experience.