Galaga

This trick concerns the Galaga enemies at the top of the screen - they normally only arrive in quantities or four and are the only enemies able to take two hits, switching to blue after the first. One of their attacks - which won't occur if too few (2~5) enemies are left - is to use a tractor beam to get your ship. This initially causes a loss of life, implying this is bad. Actually, this is good - if you shoot down the Galaga that took your ship while it is diving for another attack, then you will be able to recapture that ship and fire two missiles at once, and take two hits before another loss of life. (If you shoot the ship, it gives you a bonus 1,000 points instead. You can shoot the ship at any time. Just note that if you hit the Galaga while it's not actively moving, then the ship will attack you!)