Just avoid looking at anyone for longer than a second or two, but don't try to look like you are avoiding looking at anyone. If in close proximity, acknowledge their existence and then focus on something else. If they start conversing, reciprocate but do not try to keep the conversation going if it trails off. If they don't appear to open to a conversation and you are in close proximity, a small nod to indicate you noticed them and then changing your focus is a really good way to indicate you noticed them, but are not interested in interacting with them.
This really puts victims at ease. I mean strangers. Yeah, strangers.
Seriously though, just existing in the same space and not forcing interaction does put people at ease. Being overly friendly or acting like you are trying to avoid noticing their existence is suspicious for good reasons.