run as fast as you can around the whole map, wait at specific areas like the lobby every lap, save up points until rd 30, turn on traps as necessary after rd 30, use ur ray gun to make crawlers, knife the crawlers with a bowie knife
if you walk slow the rounds take alot longer and they are harder as you cant link teleporters as much, zombies spawn in front of you, and you waste ammo on those zombies spawning in front of you... by rd 40, every 5 rds should only use up half of ur ray gun ammo