I've coached a lot of newbie mixes over the last month and here is some things that I think need to change, and those that I think are good.
First suggestions
Change days of play, if you want to play on Fridays, make the next week a Sunday or something. This will get more people to coach and play, since not everyone is going to play on Friday night. Those that do seem to be the same people.
Positives
1) Stay in mumble to talk over the match after it is over. I know that sometimes it's hard since there is not a lot of coaches and you want to help more people, but slow down and talk to people before leaving. You're going to more good by teaching, not just pugging over and over again.
2) Newer players generally listen, but make sure you press questions out of them. Some people are afraid to ask questions directly.
3) Switch classes to help the people playing. For example, if someone wants to learn to be the main caller, let them. Just coach them in the process.
4) Don't allow people to try to just out DM. I see this all the time with new open teams and players, teach them that the best way to help improve yourself and your team would be to help your teammates to make everything you can be at least 2v1.
Cons
1) Stop allowing people with experience to play in the mixes. I've seen an increase over the last few weeks that come in just to stomp new people to presumably few good about themselves. Allow admins to ban people that are offclassing/trolling/aliasing for this purpose.
2) Admins also should just shutdown/kick, overall restart the pug without the shit stains that are doing it.
3) If you notice that the teams are really uneven, ask to stop the pug and switch people to make it even. Basically, utilize time efficiently to stop rolls so people don't get annoyed.
I have more, and yes I know my order is everywhere, but I kept thinking of more lol