A zombie mode server is not like a normal server. Blue plays the humans, while green plays the zombies.
Due to my recent aggravating experiences regarding zombies and other players, here's a few tips for surviving and becoming an undead nightmare on the green team.
When you spawn, you'll be holding a gun. STOP. STOP EVERYTHING. LOOK AT THE BOTTOM GODDAMN LEFT.
YOU SEE WHAT IT SAYS? ZOMBIES CAN'T USE GUNS.
"Oh shit," you think inwardly, quivering in your booties, "This is so unfair and I'm going to die!" Toughen up, you maggot-infested brain connoisseur you. You can still kill people with your shovel! The cold, dead grip of undeath has also granted you the boon of dramatically increased health!
With new confidence, you run straight into the hail of bullets known as the blue team, and are promptly put down. Again and again, with great frustration, you repeat the process, dying to the inferior, yellow-bellied humans and their BB guns.
So why do you keep running into them? Ignorance. If a bluesie is shooting at you, don't take that! You're a strong zombie that don't need no humanity! Jump off the closest cliff and stick to cover. But how do you leave cover? There's campers everywhere!
Simple.
The only way to go is up. Look at the ground, or in front of you, and smack that block with your shovel. UP you go, up high, disappearing in front of their eyes and screwing up their aim. >> Jump like a crazy black man wearing Air Jordans, and those bluesies won't hit you. << (Duck Dodgers damnit I cannot stress this enough.)
Jumping back into cover, get under them (I presume you jumped off a cliff or wall, right?) and jump up in front of their faces. Slam, wham, they're down! The brains are yours to eat for a delicious 20 health.
If that human is running from you, that's good, they are running in fear! If they are close enough, give chase, or if they have made good distance, go back into cover and GO FOR THE DELICIOUS BLUE BRAIN LUNCHBOX known as the intelligence. Once you've got it, however well guarded, jump up into a high cover and over the edge. No blue can move as fast vertically as you can. Take full advantage of this.
Should you make it back to your tent to feast on those delicious brains, you'll feel more like yourself than ever! Take this opportunity to assist your fellow zombies. Smack them with the spade if you suspect they're injured and close enough to you, type /b and check out the build options to make going around as a human more difficult (Zombies needn't worry about heights, remember?) as well as building bridges with walls on them to assist the passage of your fellow zombies. But be careful, with the abilities you gain, you also lose your phenomenal endurance, so beware opposing blues... you are the lone brain gunman.
Follow all these tips and I guarantee your zombie play will be filled with feasts and sprees.
EDIT: And for god's sake, you shamblers, don't dig any tunnels to the lunchbox. You're not some common serf zombie working for his food, you're up there super-jumping with Jesus Christ in the sky! Leave tunneling to the dirty peasant Bluesies.