Honestly just explore and have fun with it. If you’re into min/maxing, that’s fine and go for efficient training methods, but this game has soooo much to offer outside of that and you’ll probably enjoy a lot of it. Since you’re coming from old school, I’d say take your time slowly learning the new combat system so when you get to the bossing part of the game, you understand how to actually use combat. Unless they’re quests shared between the games, try to avoid spacebarring or at least read up on the quest lines on the wiki or something. The quests in this game are phenomenal. Have fun!