I'm not one for combat, for most of the games I go for story or lowest difficulty. Still, in this game you have to take advantage of stats effect (frozen, chilled, burning, or any other) which can be used for detonation. Manage your team and skills to get as much combo as you can and be aware about the enemies you encounter. Each of them have a specific vulnerability which can be exploited. I play in Story mode and Rook never die with additional disable the path warning for enemy strikes and first fight with a dragon was fun. Lots of dodge and fade steps, skills combined for max damage, potion used twice and the fight was done in 2 min.
See the skills descriptions, choose your weapon based on additional effect more than the damage and don't forget to use finisher when you get the chance (it's fun to watch and does lots of damage). The companions usually yells at you "finish it" and you should do so.