Rarely anymore do people have training partners. It's a sad state of affairs as far as powerlifting goes, so when I get a client that has a group around them, I push them to incorporate their group into training with them.
You can't replace training with someone. From cues, to working hard, to pushing your limits...it's worth saying again: you cannot replace training with someone.
So a client asked me, "when you guys are training together, how do you decide what to do?"
First and foremost, is someone getting ready for a meet? If they are, then they take precedent, meaning if they need a straight bar for squats, we're all on a straight bar. And that goes for any movement - whatever they need for that day, that's what we're all doing.
This is obvious because if I'm getting ready for a meet, I want to execute my training plan as I have it in my head, so my training partners' job at that point is to support me. So when it's their turn, I put my shit aside and focus on THEM.
As an example, three of my training partners have a meet this spring. Curtis just came off a meet and I have no plans, so the past few Sundays Curt and I box squatted with the SSB in a power rack while the other three were in the mono with a straight bar and knee wraps. Curt and I hit our training sets in between their top sets, so we were there to wrap them, spot them, run the mono - whatever they needed.
If no one is prepping for a meet, you have one of two options:
Defer to the strongest or most experienced or smartest of the group (not always the same guy so choose wisely).
or
Decide on a direction as a group- "The next 8-12 weeks is purely hypertrophy based training, or we're going to focus on heavy carries, or box squats because (insert intelligent reason here)."
It doesn't have to be the perfect plan, and it doesn't even have to be executed perfectly. My point in all of this is, if you show up and work your ass off and push your training partners, you will all get better.
And more specifically, "what do you do when it comes to assistance work?"
Everyone needs to take control of and accountability for their assistance work. If you're struggling to push yourself here, then stick with the group or tag along with one training partner -preferably someone stronger than you - and do what they do and try to keep up. If it were me, I would train with the guy that is stronger than me in the lift that we were performing that day. So that may mean tagging along with a different guy for each upper/lower session.
But this is really the opportunity for you to start coaching yourself - objectively assess your weak points, and come up with a plan to attack them. And if you're unsure of where you're weak - hammer your upper back, lats, triceps, and hamstrings and you can't go wrong - promise.