Humans: Above all, stay together. You do zero good to your team if all you are doing is wandering through the hallways of Biotec before quickly being ambushed by zombies that have been stalking you. Instead, work in a close knit group. Move toward your objectives slowly but surely. If someone is infected, do your team a favor and dispose of him. You don't want him becoming a zombie and killing your entire team in one strike. Also, bring better guns. Sitting there with frying pans and G17s you will not last for long. But if you bring a few shotguns, your chances of survival are greater.
Zombies: Although it can be fun to just rush the humans head on, it works so much better to do something like in the lobby, crouch on one of the balconies and watch the survivors pass by. If you are lucky they won't notice you and you can jump behind them and end the round in one quick strike. Try hiding around the corners in hallways and waiting until they turn the corner and maul them. This works very well if you have a bunch of guys with you in case someone is hanging right behind the group. Another thing is to use team chat to plan. Some people like to get a bunch of guys organized enough to find a good point, such as the basement with the switch, to just flat out rush the humans. Charge and hope for the best. If you do it right you can wipe every one of them right then and there.