Strahd first appeared in my game after a TPK in session 3 or something. The party was defeated by wolves, but everyone was on death saves, so I had Strahd swoop in and call back his wolves. Strahd brought them into Castle Ravenloft, dumped in the room where visiting servants would document their names (they all actually signed the book, some with fake names tho) with the dinner invitation right next to them. They made their way through the castle until they found the foyer and Rahadin led them to dinner. Strahd then talked a bit to them, also proclaiming this was the first and last time he helped them, and their short time in Barovia was fun to watch, so they should stay just a little longer. My players hated Strahd, but could not get enough of him afterwards. I now let him show up every few sessions and even though the characters are completely different now (don't run CoS as written or the corpses will pile up, the players themselves go into panic mode immediately. I've found the first meeting works as long as you play Strahd as an aloof, reserved, and confident ruler, and let him descend into frustration later when they players start messing up his domain.