When you're in battle, you have to find a good balance between getting in an offensive position where you can maximize the accuracy of your shot, and a defensive position where you can avoid damage. If your character's body has a blue striped line over it, that means they are protected. Make sure to check the accuracy before you shoot at an enemy so that you know whether you're likely to actually make the shot or not. Anything under 60 percent, and you might want to change positions.

Move slowly and keep your squad together as much as possible. They should be balanced with a scout, a heavy and a sniper. Move all of them a few spaces at a time, so that you can encounter enemies more slowly rather than all at once. It'll take more turns, but you have an unlimited number of turns in battle, so that doesn't really matter.