I go on at least one street shoot each month. Street shooting is unpredictable. It's nerve-wracking sometimes. You don't know what's going to happen or who you're going to encounter. You can look around for hours with no luck. Or you might find a great subject who doesn't want to be in your pictures. Other times I just can't seem to get going. You need to be in the zone: attuned to who and what is going on around you, but also relaxed and confident enough to approach strangers. You get into a groove approaching new people and asking if you can shoot their portrait. It's very rewarding when you step inside someone's invisible barrier and start to see the person underneath. More so when you do that then produce a strong portrait.
I think you have between five and ten seconds to sell yourself to a subject. You need to explain who you are and what you're doing while also demonstrating that you can be trusted; that you're safe.
Telling people I'm shooting portraits for a project called Faces of Brighton has been a great help. People intuitively understand what I'm doing. The name of the project makes sense to them. Almost everyone I approach seems happy to be asked once they understand what I'm doing. Sometimes, very rarely, someone will politely decline. I met a little old lady on Brighton seafront recently who immediately struck me as a unique and fascinating portrait. I explained who I was but she simply said, 'No, I don't think I'd like to do that. I'm sure you'll find lots of other people who would.'