You SHOULD NEVER never shoot an LEO first! There must be valid reason to pose a threat to an LEO.
(1) You CAN NOT shoot at Police unless they aim a lethal weapon towards you first. The only exception to this rule is heist scenarios where you do not have a hostage.
This rule is in effect to ensure that role-play scenarios are NOT cheap and that would encourage more people into talking instead of shooting
Make sure that you are using COMMON SENSE at all times! Value your Life!