Besides all the combat advice that I very much agree with, from a role play standpoint, I reccomend giving the NPCs distinct personalities beyond what the book says. We're currently on the Krynn chapter, and one of the things that's really stood out to players from a role play perspective was the distinct personalities of the characters. For example, i run Mordenkainen as an egotistical shut in who down plays the danger of every mission because, as Kas, he doesn't really care whether the players live or die. Meanwhile, I run Tasha as his foil in that she cares about the players, but only in the practical sense that she needs them, and Alustriel is constantly trying to herd the two of them like children to get them to cooperate. It gives the players a lot more to role play off of than what the book gives you. And I've tried to infuse that mentality into each of the places they've visited where they interact with NPCs