I have a trick. Soon after I meet someone, I scribble their name and some interesting characteristic of theirs into a Google Docs document on my phone.

e.g. Anna, teacher with dreadlocks.

Then the next time I see them from afar, I whip out my phone to refresh my memory. And then I go up to them and say hi.

I rarely forget details about a person, so making conversation is not hard. It's their name I keep forgetting. Writing that down has helped immensely.