This is not something I do often and I do not really have beautiful examples to share, however …
I am not a wedding photographer, so I do not need the full list of the bride, the groom, the parents, lined up like ducks … I'm free to photograph this that I like.
Usually, if I shoot in a crowd or a gathering of people, I will tend to step back and pick individuals or small groups with a long goal, shooting straight rather than posed.
Sometimes it's separating them as being the only person or small group actually focused – wide opening helping with dim light as well as separation; Sometimes I frame them almost exclusively, cutting everyone out.
I always try to use the light, even if it means that I can not have so many guards. I am not a fan of how the flash kills the atmosphere.
The alternative is to take wide-angle shots so that everyone is in the frame, I always think I could do it with a phone – so I tend not to do it at all. If I do, it will be a quick edit, get people to look that way and smile – but it will look like a "happy shot" most of the time.