To zoom in twice with a sniper rifle, hit L and then click the right analog stick.

Haul More People on Vehicles:

To get three or more people on each vehicle, and have other players jump on the car while it's full. Then, the players on top of the vehicle will need to duck and they should stick on the vehicle without falling off.

Quick Turbo Recharge:

If you've used up your turbo in a vehicle and you want it to recharge very quickly, get out of the vehicle and hop back in. Upon re-entering, the vehicle's turbo will be fully recharged.

Hint-Kill The Queen & The Caretaker Fast:

For the spider queen when you first go in, get one person (on Co-Op) to go down on the ground. Then the Queen should come out. When you first jump off the ledge you come from there should be another ledge below it connected too pipes leading to the first ledge, the person going down will activate the Queen to come in then quickly turn around and jump onto the 2nd ledge (Might take awhile but it works) then the Queen will be trying to get you from the 2nd ledge. The person on the 2nd ledge shouldn't fire yet, get the person on the first ledge to fire and distract the Queen then the person on the 2nd ledge will jump down, (If your out of ammo there should be some ammo lying on the ground) make sure the guy that's up on the 1st ledge has the Queens full attention before doing this. Get the guy on the ground floor to get the grenade launcher out, use the incendiary grenades or the flamethrower too set the queen on fire which should quickly kill her faster than you both jumping down and trying.

Hint-The Caretaker: