Mine, when I do it, is chapter and verse. I first (half an hour before the game) check with both coaches whether they have experienced front rows. If either side doesn't, then my PMB will be about 5 minutes later, and take 3 minutes or so. All FR to attend, SH optional.
"Hi, does anybody not speak Dutch? Ok, during the game, I'll speak English, but for explanations I will speak Dutch. Hookers? ... Ok, you are in charge of helping me keep the scrum safe. On 'Crouch' you can ask us to wait. Keep your shoulders level with your props. On 'Bind', I want your right ears to be roughly above the mark I have made. Props, make a long bind on your opponents at this point, but stay ear-to ear. Once you have bound, I will call 'Set' , you will move shoulders to the line where your ears were, and the scrum-half will put the ball in soon after at my signal.
"I want to see a straight drive, the scrum turning on the spot is a clear sign of an illegal wheel and it is potentially dangerous. The natural clockwise turn (torque) is fine. [Remember, at your age a maximum of one-and-a-half metres, and same side throws in again if it goes more than 45 degrees]
"Remind the back row to stay bound, oh, and while you are here: Just a reminder that although the law requires you to place the ball immediately when tackled, if your own players are there to form a ruck, I'll allow you to take longer than if you are isolated. So the same action may be tolerated or penalised depending on whether support is available or not. Similarly if you are the tackler and you make every effort to roll away or at least let the ball out even if it is difficult, we'll play on.
"Any questions?"
"Sir, when is the ball out of the ruck?"
"Ok, first of all, I will let the scrum-half use one hand to dig for the ball. Both hands on means he's able to pass and must do so within five seconds; if necessary I will call 'use it'. However, defenders not in the ruck need to stay behind the back foot of their own side of the ruck until the ball is lifted from the ground. Any other questions?
"OK, you've still got <20> minutes to prepare. Please send your captains to me for the toss in a couple of minutes."