Even though we use replicas in Milsim/Airsoft we treat them like real firearms. It is imperative you know and practice the 4 Rules of Firearm Safety.
RULE #1: Every gun is always loaded!
RULE #2: Never let the muzzle cover anything you are not willing to destroy.
RULE #3: Be sure of your target. Know what it is, what is in line with it, and what is behind it. Never shoot towards anything you have not positively identified.
RULE #4: Keep your finger off the trigger until your sights are on target.