Turn up the battle speed to the highest setting

As our final stop on the “do this to improve your quality of life” train, go ahead and pump up the battle speed settings to “Ultra-Fast” right away. Battles in Dragon Quest III HD-2D move dreadfully slowly by default (even compared to past versions of Dragon Quest III), and you don’t necessarily need to read every letter of battle text to understand what’s going on.
The only exception is if you use a Gadabout, as you probably won’t have enough time to read about the antics your ne’er-do-well companion is getting into. But, also, maybe don’t start the game with a Gadabout either. Consider that a bonus tip.