Basic Firearms Safety - P.R.O.V.E.
In order to make sure a firearm is unloaded, following the acronym P.R.O.V.E. will ensure that you don't miss a step!
P - Point muzzle in a safe direction
R - Remove the magazine (if you can)
O - Observe the chamber
V - Verify the feeding path is clear
E - Examine the bore (Use a cleaning rod / camera / bore snake)
By memorizing this acronym it will ensure that you don't miss a step in ensuring a firearm is unloaded in a safe manner.