When I want to learn a bunch of people's names if we're, say, all part of a class or seminar or meetup, I'll pull out a piece of paper, draw a square/circle/etc to represent the shape of the space we're gathered at, and then subtly write down each person's name as they introduce themselves. This way, I can remind myself of everyone's names based on their physical position.

Additionally, if people are taking turns introducing themselves in long form, I'll go through each previously introduced person's name in my head, looking at them as I think about their name, as the currently speaking person introduces themselves.