Spray'n'Pray, or the uncontrolled, constant burst of fire, is not the name of the game in Xenoraid as your guns will overheat. Control your shots and fire in small bursts.

As each mission has four ships, and repairing them is much cheaper than buying new ones obviously, you should always revolve them mid-combat when their health gets low.

When upgrading at first you should focus on one or maximum two ships, max them out and then proceed to upgrading the others.