You may know your neighbours and the person who delivers your post and the police officer who walks round your area, but if you don't why not say 'Hello' and that will you started.
Or you may be a 'Hi' person, or prefer 'Hiya'. Or like in the East End you might extend an 'Alright?' Whatever way you make contact with people doesn't matter, what is important is the connection of community. And there will always be people marginalized. On the edge or outside.
That person who lives near you who always seems on their own. In the post office queue you notice they are sending parcels abroad to the only family they have. Or at the supermarket they always pick up meals for one. Maybe you see them at the cemetery visiting their lost loved ones. Or they are that person spending a lot of time in the library, or feeding the ducks in the park or nursing that cup of tea. What harm can it do to say 'Hello'? And what good could it do to acknowledge another person and their place in the world? It may be the only human contact they have. The least you can do is say 'Hello.'