Let My Poor Voice Be Heard
Once you become comfortable playing in front of people, the next step is to capture audience attention. As with getting used to playing in front of people, the best place to do this is open mic nights. The methods should be unique, as they should not tarnish your brand / your music.
In general terms, you want to invoke a strong emotional response in the audience. The response should be so strong, that you cannot help but listen. This is why an open mic night is the perfect place to do this. People at the coffee shop / bar mostly did not come to see you. They came to see their friends, or to have a coffee.
Its your goal to polarize these people's emotions, and get them to listen to you. Any emotion is fine at the onset. Just get them listening. Then the trick is to convert those emotions into liking you.
This is a two step process, and you should start by experimenting at the polarization. If you are not failing at it, then you are not polarizing enough. Once you can polarize, then start practicing your conversion.
Its more important to polarize than for them to like you. You can always convert a hater later.
All Eyes On Me
If you are playing regularly, the best way to make this switch is by adopting the mantra all eyes on me. If you look out into the crowd, and people are not looking at you then you failed. You need to polarize more. Iterate over that.