Instructions
Stab incoming zombies with your knife in the first few levels to save your ammunition. The zombies early on are easier to kill, so a knife will get you points while the ammo becomes more useful later. Every knife kill nets you 130 points. In later levels, shoot the zombie several times in the body and then knife it to death to still get the 130 point knife kill if you have the ammo to spare.
Purchase the "quick revive" upgrade as soon as you're able to from the upgrade menu. The upgrade allows you to revive teammates faster while also allowing teammates to come to your aid in a shorter period of time if you are wounded. This aids you in staying alive longer, which will result in you scoring more points as you kill more zombies.
Shoot for the head once ammo gets scarce. Head shots kill zombies faster with less ammo used than body shots. As a result, you'll save more ammo and can kill more zombies for higher points.
Stay in the starting rooms in the first several stages to maximize points by killing the endless swarms of zombies that keep appearing there. They are the easiest targets and the more you kill, the more points you score. Once you're satisfied with your point total, move out of the room and into the rest of the level.
Repair barricades as soon as they are damaged. You get 60 points for every fully repaired barricade and this helps prevent you from being swarmed on by zombies.