Start by talking to people you have on interest in talking to. Don't approach an attractive member of the opposite sex or a businessperson. Instead, say hello to an elderly person you normally wouldn't look twice at.
Or try to make cashiers laugh. Brighten up people's day. If you just talk consistently, you'll get better. Talking to people is a skill like any other.
So yeah, say something to the cashier. Ask the barista if they changed the chairs. Ask the guy who takes your parking ticket if he knows a good restaurant. You have to make a beginning, trite as it sounds, and no beginning is too small to help.
To learn, you need to be able to try a lot, in a consistent environment, and get feedback. Bars made it difficult to try small things, and they're a complex environment where you can't repeat the same interaction so easily.
Whereas, saying "hi" to a stranger is never that different, in terms of how it goes initially.
Whereas, when talking with people on the street, I don't care how the interaction goes. So that makes me relaxed, and the interaction goes well.
I enjoy it for the sake of it, whereas I don't enjoy clubs unless things go well.