Don't bother trying to terrify your players; just play Strahd like he was your own PC, and terror will come naturally. However, if you want to work on a mood that will put unease into your players, remember that it is the unknown that causes the greatest fear. Was that howling wolf just a wind beast in the distance, a messenger of Strahd or Strahd on the hunt? Why does Madame Eva shake her head in sorrow when she first spies us? Does she know something about what will happen to us? Who is the little girl who stands over a mother's grave, and does she have fangs, only to vanish in a swirl of mist rising from the ground?
Don't ever pick a fair fight - Strahd should never show up to fight the PCs directly unless he has to, or until the party is already knee deep in other monsters. He's been around the block for 800 years; he has time on his side, he can afford to be slow and methodical, waiting to strike once the PCs make a mistake. Have him swoop in, make a strike or two or drop a spell to confound the PCs, and abruptly leave, even should he be winning. He should play a game of attrition and "shaking" the party up. Assume he always know what the PCs are up to unless they specifically take measures to thwart him, and that he's never more than a round or two distant from the PCs to strike. Never give a lone PC a break - Strahd should take the opportunity to move in on such PCs. In many such cases, domination of the lone PC is a better tactic than an aatack. He can then use that PC to lure the others into traps, ambushes or betrayals at the right moment. Change Strahd's spells to ones that favor him and would be more effective against tactics PCs may attempt.
Want to strike the fear of Strahd into them? Have him constantly interrupt any attempts to rest - preferably throwing minions or summoned wolves/bats to harrass the PCs. When they can't rest to regain spells, hp and the like, they'll stand up and take notice.
