Here Matt Graham of Graham Combat demonstrates the right way to engage a target with a pistol from inside a vehicle. Matt not only shows you how to draw and fire from the side of the vehicle, but goes into how to shoot through the glass and follow up.
There is also a demonstration on shooting at your target from behind the vehicle but at the ground level, this all depends on the circumstances. The demonstrations highlights shooting from modified prone and crouch(head to the ground).
As always these are tools are meant for you to take with and polish to help you survive. More information on Graham Combat here.