Resonance of Fate pissed me off so much... but I slowly started to understand what I was doing wrong through trial and error (the tutorial and HUD text is so small I can barely read it, and I'm not exactly an expert on this style of game) but now that I've got the hang of it and understand how to level and fight, I'm enjoying it immensely :)
My favourite option is the Tri-Attack. Must attacks involve you running. When you plot a run course, and it crosses the line between your two allies, it'll give you a Resonance point. You'll lose that point if you do anything other then a Tri-Attack next turn, or earn another R point next turn.
So if your fighting a boss, your three characters will criss cross between each, softening the boss up and also storing Resonance points. Once you have three or four, you stop your criss cross attacks, and you now form a triangle. Depending on how many Resonance points you've amassed, you'll run around the enemy in a synchronized attack that many times.
You'll dodge all of their weapons fire and dash around and over them, pounding the living shit out of them with a threeway hail of gun fire.
A did this with a Tree monster, and we ended up blowing all of its armor and limbs off, and then the grenadier tosses a molotov cocktail in the air and backflip kicks it at him. Boom.