not to nit-pick but thats the wrong order to quote them in. if he follows that order he will never hit anything.
steady position
cheek weld
sight picture
breathing
trigger squeeze
also saying that paralax on airsoft optics matters is like saying snow camo works in the summer. the groupings sorry pattern of an airsoft gun are so huge at distance that a thing like paralax being off by 20 yards won't matter. look, dont worry about paralax. if youre using a red dot or reflex there is no paralax adjustment. it is typically 0 to infinity anyway.
sight through the optic at whatever distance you will be shooting most of your targets with your right eye (30 yards or so is typical) and adjust your optics to the BB strike. after your done doing this, sight THROUGH the optics again at the same distance with your right eye and simply open your left. keep looking at the target. now squeeze the trigger. you will have hit the target, and used both eyes to do it.
the most important thing you will need to remember is that you need a good foundation to build a house. the same is true of shooting. if your base or position os off the shot will be too.