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

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.

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.