Survivors:
1. Before you go anywhere, talk to your team about where you plan on going to make sure everyone is clear. The last thing you want is half your team to go one way and half to go another way. A separated team is a vulnerable team, and the infected WILL use it to their advantage if you split up.
2. Close doors behind you. I know this sounds trivial as the infected can just knock them down but it serves as a method to slow them down and give you a warning that something is trying to sneak up on you. You see something is knocking down the door you just closed behind you? Shoot it a few times. If you manage to kill it you'll be glad you did.
3. Listen for audio cues. The witch music should tell you to turn your light off immediately, the tank approaching music should get you taking out your molotov and finding a nice, open area to fight the tank in, and the sounds the special infected make should get you on your toes for an attack. Remember, the boomer hides and ambushes the survivors, and the hunter and the smoker attack from the top of buildings generally. Be aware of your surroundings.
4. Just because the minigun is there, that doesn't mean you have to use it. I know it looks tempting but there is usually a more easily fortified position somewhere else in the map. Typically indoors is better than outdoors since it minimizes the angles that the infected can attack from, so think about that the next time you decide where you will make your stand.
5. Be alert. Make sure somebody is watching on all sides. If you are in the back, watch the rear and warn your teammates of any special infected you see. There is nothing more annoying than a boomer vomiting on everyone because nobody was watching your back.
6. Cover each other when getting an incapacitated comrade up. The infected like to use incapped survivors as traps so make sure somebody is watching for boomers and smokers when getting your teammate up.
Infected:
1. It is just as important that the infected team use teamwork as the survivors. If everyone just attacks by themselves the survivors will probably make it through just fine, but if everyone attacks together, that is when things get deadly. Work with your team and you will win.
2. Know your role on the team. The boomer must hide and ambush the survivors by either vomiting on them then running away, or putting himself into the line of fire so he will explode near them. If you choose the second option, try putting yourself between the survivors. This puts them in a difficult situation as they cannot just shove you in one direction then shoot you, and it usually ends with you exploding on two or more people.
The hunter is the primary DPS of the infected, but he cannot just attack the survivors when they are all together in a group. All that will happen is he will be killed quickly without doing much damage. Wait for the boomer to vomit or for them to get separated. That is when you will do a lot of damage. Also, you don't always need to pounce. Your claw does a lot of damage by itself, so a good tactic is during a horde just run up and pretend you're a common infected and start clawing away at the survivors. Often they'll be incapacitated before they realize what's wrong. The smoker, much like the hunter, has to choose his moments. Your tongue can be easily defeated. They can simply melee the survivor, shoot the tongue, or outright kill the smoker. So, you need to wait until you are pretty sure they will not be able to save your victim immediately. Also, you can use your ability to pull survivors to pull them into traps such as car alarms or witches. You can also pull them off ledges, which is very effective as long as his teammates can't just immediately pull him back up. Finally, the tank can be a make or break moment for the infected team. You want to be constantly keeping the pressure on as a tank, while all the while keeping an eye out for opporitunities. If you see a cliff, try to knock them off of it for an instant kill. If you see a smashable object(outlined in red) try to him them with it, since it knocks them down with one hit. If you do knock down a survivor, don't just stand over them and try to kill them. They will just chip away at your health and it won't be worth it. Instead try to knock down the rest of the team. If your teammates are good they will help you, so let them do so. If you see a hunter has pounced on one of the survivors, leave him alone and go for his comrades. Just because you are the tank doesn't mean you're invincible. You still need your teammates' support.
3. Cover each other. If you are a hunter and you see your smoker teammate has a survivor by himself, don't pounce and steal his kill, instead cover him. This means stay crouched and wait for another survivor to come along and try to save him, then pounce on him before he can do so. Not only will you do some damage yourself, but it will delay the survivors in saving the first victim, and thus increasing the amount of damage done and possibility for an incap or even a kill. The same goes for even the tank. The tank, regardless of how good he is, can not take down all of the survivors himself if they concentrate their fire on him. A boomer vomiting on them will do wonders for a tank as it slows them down to a crawl, allowing the tank to run in and finish them off. Also, the tank typically has people running for their lives and often leads to the survivors getting separated. Use this to your advantage as a hunter or smoker. If the tank keeps the pressure on enough, your victim's teammates will not be able to save him.