How do you decide who to follow, who to pass etc?
I go out with whatever group of bikes I happen to get in the staging lanes. I run a warmup pace lap for their tires/mind, then I will pick up the pace a bit, and look back to see how they're doing.
If they're looking good, then I'll either pick up the pace a bit more, or I will wave them by so that I can watch their lines, body position, smoothness, etc. If they're doing well, then I may just let them go and pick up whoever is behind them. Same drill for them. Wave by, and observe.
Passing is done for different reasons:
1. A slower rider that's smooth, but is working on their skills. I'll pass to let them have their track time, or I might show them some lines and see how they're doing.
2. A rider with poor lines and/or "on the edge": I will pass and help bring the pace down a little, then show them lines, and smoothness.
3. The fast rider, close to the bump: I will follow them to observe, then I'll pass them for a few pointers, then wave them back by to observe again. This may happen several times within one lap. If we've talked in advance, then I may pass in places where they are leaving me room to pass just to re-enforce the use of the track.
4. Sometimes I will see someone make an illegal pass/move, and then I'm passing others (within the group rules) in order to catch that individual.
There's so much going on out there that sometimes you just wing it, and help whoever you can while trying not to hold anyone up. Other times you're tired, and just wave people by for a lap to take a break.