Instructions
Choose a gun that complements your playing style. If you are a poor shot, go for a machine gun that allows you to spray bullets in the general direction of the zombies. If you like to kill with one shot so that you can run quickly to the next area, choose a high-damage weapon like the shotgun. You can find guns on the walls of combat areas.
Don't run out of money. The purpose of having money is to buy better guns and to open new combat areas, which will allow you to progress to higher levels in the game. Without money, you don't progress, so shoot as many zombies as you can and replace as many barricades as possible before running to new areas. Also, only buy guns when the new option is better than the one you have.
Kill clusters of zombies instead of wasting bullets using grenades. There's nothing more deadly for the player in this game than running out of bullets or being overrun by hordes of zombies.
Watch your own back by backing into corners. This way you only have to watch your left, right and forward areas for advancing zombies. Make sure to look up as well, since some zombies tend to come through the ceiling.
Follow directions. There's no need to guess at what to do next in a level. Follow the directions written on the walls in each battle area. Getting to the next area quickly without erroneous turns is important to your survival.