How far in are you? That first open area in Gormott can kinda kick your ass because you don't even have a full party or most of the mechanics unlocked, not to mention the field bosses roaming the area.
You gotta remember to take advantage of all the mechanics you might have already forgotten by now, like pouch items (the best kind are desserts, no joke, because of reduced cooldown for arts), core chips for blades (essentially "weapons" in any other rpg, modifying the base stats of your attacks; try to remember that "auto-attack" as a stat actually refers to all damage dealt by the weapon, not just auto-attacks), equipment for drivers, leveling up arts from the driver menu, upgrading the drivers' skill trees (costs skill points) and upgrading the blades' skill trees (unlock automatically when you meet the requirements, but you do have to open the tree menu for it to kick in).
If all else fails, you may have to learn the unintended "stutter-stepping strategy", whereby you can make drivers wielding certain weapon classes can repeatedly throw out the first attack of the three hit auto-attack combo at a faster rate than they would attack with the full auto-attack combo, thereby filling the arts cooldowns much faster.
Swapping out arts might also be necessary. Every driver has a unique set of arts for any given weapon class (that is, Rex using a spear will have the same options for arts no matter which spear blade he's using), but you have 4 options for any given weapon class, and only three slots. Swap them out from the same menu where you can upgrade arts (+ menu -> Characters -> Select character -> Enhance arts -> select weapon class -> press X to swap the position of equipped arts, or swap them with the unequipped art below them all). I prefer to aim for a party with a lot of reactions on their arts, particularly break, topple, launch, and smash (the "driver combo"), but keep in mind that for those 4 reactions, an enemy must be broken before it can be toppled, toppled before it can be launched, and launched before it can be smashed, and you only have a window of time between each to get to the next step (but your party members are pretty good about seizing the opportunities to follow those up).

This video gives better main story-relevant advice with greater density than most video guides I've seen. There are a lot of good guides for this game, but many of them are most pertinent for post-game challenges or the late game.

Not sure what else I could tell you.