Honestly, there isn't a whole lot you can do in terms of quest variety. However, the game does a fairly decent job of at least trying not to slam you with the same format of quest over and over again in rapid succession. The story tries to break up the assorted fetch and kill quests with dungeons and/or trials.

If it ever gets a bit too grindy, there is still plenty of other things you can do on the side to help recharge your batteries.