LPT: If you're ever in a conversation circle at a social function, keep an eye out for people trying to get in and get them up to speed
This feels like a common courtesy I don't see enough, particularly the second point. In a conversation circle, always try to keep your side vision open to people trying to find their way in. It can be awkward to try and find your own way in so giving them a spot tells them they're included then drop a quick brief on the conversation "We're talking about pineapples on pizza, good or bad" gives them context to jump in immediately.
If there isn't that special, outgoing and kind of goofy person in a group to do what you are saying, groups of fairly good intentioned people can just feel incredibly mean and unwelcoming. It is really weird when you are the new person and can see the group desperately needs people to be aware of these things but no one cares or is aware of it. Every one of the people in the group can be a friendly person but the group is effectively a mean clique.
I guess I’ve never thought about it. I have to admit, without realizing I was fortunate, the circle almost always just kind of open to let me in (just listen to catch up) or if I wasn’t noticed I’d just bully my way in there with “move over! I want in in this” with a smile and kind, nudging hand on the shoulder or back.
I will definitely try to be more aware
I’d also like to add: read the situation and adjust your etiquette accordingly. For example, I personally think it’s pretty damn rude to interrupt someone. However, with some groups, interruptions are just an expected part of the flow of conversation. Try not to be weirded out by harmless etiquette differences that others seem to be taking as normal.
I recently was at a party and was kind of shocked at how many people don't follow what I considered to be the norms of group conversation. When a conversation circle forms, I think it's polite to acknowledge other people. If someone new joins the circle, at least say hello or acknowledge them with body language. It's uncomfortable to walk up to a circle and feel iced out because no one even looks at you. I also think it's rude to monologue or tell everyone your whole life story. It's appreciated to engage with other people, and give them the opportunity to talk.
I think some of the people were just socially awkward and clumsy, but I also suspect some people are still mentally High School and were ignoring other people on purpose.