Hobbies And Interests
Early Rounds
For the first three rounds of the game, you'll have only a few rounds of zombies to deal with. While it's not much of a challenge, it is a perfect opportunity to rack up the points necessary to buy better weapons. To maximize your points, let the zombies break through the boards and enter the room, then kill them with the knife -- this will net you more points than simply shooting them. After the third round, there are too many zombies swarming to make use of this strategy. But by this time, you'll have amassed enough points to unlock more-serious firepower.
Defense
Using your free seconds to board up windows is essential to your defensive strategy and can buy you lots of time for when the zombies are attacking from all sides in the later rounds. A way to ensure you have enough time to board up every window between rounds is to kill every zombie but one, then blow off its legs with a grenade. While the last zombie slowly crawls around, and with no others attacking, you'll have plenty of time to board up each entrance.
Offense
If you see a power-up drop midround, grab it as quickly as possible as they disappear after 30 seconds. These power-ups can give you an essential offensive advantage in later rounds. The Insta-Kill power-up allows you to take down zombies with a single bullet, ammo boxes replenish your supply and Napalm will wipe out all enemies in your immediate area. Otherwise, equip as strong an automatic weapon as you can afford and go for head shots -- you'll take them down quicker, earn more points and use less ammunition.
Mystery Box
Once you've racked up a considerable number of points and can easily spend 1000 with at least another 1000 left over, open the door with "HELP" written on it on the far left of the map. Here, you can purchase the "Mystery Box" for 950 points, which affords you with a rare, powerful gun such as the FG42 or the ray gun. While you're here, try shooting the radio -- you'll be rewarded with a random selection of in-game music.