There are a few threads as noted above. I used to be guilty of the long linear pre match covering all restarts, but have really stripped it back recently.
I emphasise 2 main things at the start
1) Accurate identification of KMD's
2) Credibility
I then briefly cover the following:
1) GK in possession - either no attackers around the next KMD is likely to be ball coming back for offside, OR if there are attackers in vicinity the potential KMD's are attacker infringment in which case we want to penalize quickly before they score and start celebrating or them gaining possession legally and potential defensive infringements such as DOGSO (KMD accuracy, Credibility)
2) Eyes on me for all throw ins, even in their 3rd where I'd want them to lead in case I've spotted a flick they haven't. If I have I'll be giving them a lead. Outside of their third, I'll typically lead, but if I'm unsure I'll be looking across for their input - if neither of us are sure, we go defensive. (Credibility)
3) Delayed flag on offside decisions to ensure its the player in the offside position then committing offence (avoids messy decisions with secondary runners from deep). Only time I want a quick flag is 1-1 with keeper where potential for a clash. (KMD accuracy, Credibility)
4) Free kicks - I define their credibility area (typically to the edge of the penalty area and about 10 yards into opponents half) and ask them to look at my positioning before giving me anything outside of that area. I also ask them to match my tolerance for little pushes and pulls for consistency (Credibility)
5) Penalty kicks - I want first bite at all penalties, I'll invite you in if I want your input - emphasise worst case is me waving a shout away and AR flagging for it which kills our match control. Also if there is a quick break the AR is likely best placed to identify the marginal inside/outside the box. Help me by either going to the corner flag for a penalty or a few steps towards halfway for free kick. Emphasize importance of this as it's potentially difference between a yellow and a red card (KMD accuracy, Credibility)
6) Mass con - take a position to get a view. When we come together please give me Shirt Colour, Shirt Number, Offence Committed and Recommended Sanction e.g Red 7 has punched opponent, so VC, Send Off. (KMD, Credibility)
Final point I always make is to enjoy it!