HINTS / TIPS:

If the game runs slowly on your computer, right click on the game and select "Quality" and then select "Medium". This will make the game a bit more ugly, but will result in much smoother gameplay.
When you run out of ammo, click the "RELOAD" button on the lower left.
There are special hidden power-ups throughout the game with give you more ammo.
Your final ranking is not only based on score, but on your hit ratio as well, so try not to miss.
Cliff Yablonski probably doesn't like you.