I find headphones are always good for public transport etc. I always try to position myself in a strategic spot. On the tube line (subway) I live on, the train seating is arranged in a specific way. I know which carriage will have the seat I like which means people don't usually sit next to me unless it's really busy, and I don't sit in the sidways facing seats so that way I don't have to look at people.
I find that's about the only situation I really struggle with now. In supermarkets or when out shopping, I just try to focus by using lists, and headphones again. Other times I'm not really in close enough proximity to people for long periods of time.