Hello.First of all i will talk about weapons.
Weapons:What weapons should you take when playing as a human.
Shotgun:
Advantage:Very good at close combat.You can kill a lot of infected with 1 bullet.You cant run out of ammo.
Weekness:Week at long range.Reload time is long(if you dont know when to reload).
This will be the best choice as almost all fights are in closed spaces and you dont need to worry about ammo.
Machine Gun:
Advantage:Good at close range and long range.
Weekness:You must reload a lot.You run out of ammo very fast(even if you preserve your ammo you will run out of it eventually).
This is the second choise as a weapon.
Sniper rifle:
This weapon is useless.It is good at long range and week at close range.You should not use this weapon at all.I would take a machine gun instead of a sniper rifle.
There are 2 option of how to arm you and your teammates up:
1.3 players should take shotguns and 1 player should take a machine gun(this is the best choice as you have very good close combat damage and when needed long range).The one who will carry the machine gun must preserve ammo as much as he can(shoot at head to kill enemies without using too much ammo).
2.All 4 players should take shotguns(the 2 choice as you have no long range power but the best close range).
Now i will talk about tactics against infected bosses
Boomer:If you see a boomer in front of you just shove him of at a safe distance and then shoot him.If he suprised you and he vomited on you go to the nearest corner and just shove till you can see clearly(your teammates must regroup with you at that corner and help you killing the zombies).This is also very usefull when trying to fight a lot of infected.Just regroup at a corner and kill everything that moves.
Hunter:The best strategy is to stay together and he will be harmless.
Smoker:The same as at hunter.
Tank:If you have a molotov just throw it and he will be set on fire then run(dont look back) and without shooting a single bullet he will die.If you dont have a molotov just gather your team and shoot him till he dies.
Witch:The best thing to do is to sneak around her(dont use flashlights and keep you distance).If she stands in your way just move very slowly without flashlights(you + another teammate,both of you equiped with shotguns) untill you are close enough and then aim for the head.
I hope you all learned something out of this.Oh and another thing that is critical...STAY TOGETHER!