Make sure he adjusts the rear axle so the front and rear sprockets are aligned. (very important) It helps to have the same point of reference on both side that way you can measure each side to that point to align things. You can also take off the chain and run a straight edge from the face of the front sprocket to the face of the rear, if possible.
Once things are aligned, put on the chain and tension each side with small equal amounts until there is about 1/2" of total slack on the top of the chain. This 1/2" measurement is when you have the swingarm pulled up in a straight line with the two sprockets. This would be putting the assembly in a position that the chain is in the tightest point it can be in. I like to use a cargo strap to hold it there while on a stand, but you can just keep lifting it to that point but you will have to remove the shock to do this.
Once you have the alignment and the sag correct, tighten the jam nuts on the chain adjusters. ( I like to put a little never-sieze on the bolts before I start this process)
Once you have the chain porperly adjusted, you can put the bike down on the ground in ride mode and see how much the chain lifts up on top, just in front of the top chain guide. (how many fingers fit in there) This will give him an idea of when he needs to tighten things up a bit.
Recheck everything.
Be sure and loc-tite the sprocket bolts before you start. They are notorious for comming loose even when loc-tited.
I can't stress how important it is to have the sprockets aligned, if not it will eat chain and sprockets real quick.
Hope I haven't confused you, it is a simple task once you've done it a time or two.