I recommend that you practice the "shoot 'n scoot" attack modes - shoot while retreating, and if any of them look as if they're going to get too close, hit "Return" to enter turn-based mode, turn round, go back to real-time mode, and run like the proverbial striped-tailed ape to open the range again. Then hit "Return", turn round in turn-based mode, hit "Return" again and resume firing.

When facing monsters with ranged attacks outside in open country, try shooting while moving sideways. It doesn't help your accuracy, but it destroys the monsters' accuracy. They shoot at where you are when they let go, and by the time the missile arrives, you've moved.