Always remain in cover, and look for the best cover positions. You will usually can cover left, middle, and right. Keep moving from one position to the another to have a better chances of eliminating your enemies. Because enemies target you slowly, if you keep moving you can remain out of their aim. Timing your movements depends on the type of enemy. If it is a Gunner, it is best to draw fire to an area, then quickly move two sides to the left or right. If it is a Blaster, wait until the last moment to move.