I Don't know if someone has covered this previously, but for the benefit of those who may not have access to an FAL Factory Manual, here's the skinny:
Setting the Gas Regulator is a pretty simple simple procedure (much simpler than taking the trouble to read about it) and is done using an empty magazine from an open bolt.
Turn the regulator sleeve until it is in the fully forward position - against the gas block. This position will cover the gas escape hole and will result in a maximum push against the piston and bolt. If the rifle is always fired in this condition, it tends to be hard on the action parts with most types of ammo unless you utilize a recoil buffer to absorb excess bolt energy.
From the above position (position 7) open the regulator sleeve one full turn to position 1. This normally results in a "short recoil" condition, where the empty case will either not eject, or the bolt will fail to pick up the next round from the magazine.
Adjusting the regulator sleeve back towards position 7, a notch at a time after firing single loaded rounds, will soon result in an adjustment where the bolt will latch in the open position. Fire several more individual rounds (single-loaded) to verify that none exhibits the "short recoil" condition.
This indicates the correct setting for your rifle and ammunition, but FN suggests going forward by two additional clicks to establish a margin for safety and reliability.
A special spanner wrench is available for turning the regulator sleeve, but you can also use the bullet nose of a military cartridge for making these adjustments. I use my fingers for this (if the rifle is reasonably clean) but be aware that the regulator sleeve can become quite hot with continued firing and adjustments.