Consider carefully whether you want to get involved in open-world PvP before playing on a PvP server.
One of the biggest differences to consider with WoW Classic is that the servers are structured differently. In Classic, there are PvP and PvE servers. Once you start a character on one of them, they'll be stuck there unless you pay for a character transfer. Consider carefully whether you want to get involved in open-world PvP before playing on a PvP server. It'll mean you'll often get attacked, which can be really frustrating when you just want a relaxing evening of questing. On the other hand, that extra element of danger can make the world more fun and offers more opportunities for social interaction with other players.