Try not looking nervous when you have an anxiety disorder!!!
I find that using an obviously old camera helps with street photography. A modern-ish SLR from even the 80s doesn't look that much unlike a DSLR to the untrained eye. Not that it should make any difference whether one is shooting with a phone, DSLR or speed graphic....but in people's minds it does. I have been accused of being a peadophile for taking a film SLR to the beach while enjoying a day out with friends and family. "You photographed that child in his swimming trunks"..."err, yes...he's my friend's son."....."oh...but you have that long lens, you could be photographing anything"....."Yes, I could...but I am not....I am photographing the party I came with and some nice shots of the planes flying overhead and the boats in the distance"...."You could be up to no good, I'm of a mind to call the police"......"Go ahead, I have every right to photography anything I want in a public place
It's that last but that people don't understand. At least in the UK, one has the absolute right to photograph anything that is in - or can be seen from - a public place. Yet I have come across people who don't understand this. Earlier this year I rested a 60s film camera on a wall to take a long timed exposure of cars going by....a teenage boy who walked past noticed and accosted me, "You can't take my photo"....."I wasn't."....."I heard it click. Delete it. You can't take my photo"....there followed an explanation of film, what I was doing and the kid still didn't believe that it was lawful to take a photo in the street. So I pointed out that he must surely do the same with his phone....
Generally I don't photograph specific people, I am looking to capture street scenes...life as it is in the moment. If that means people full of tattoos then so be it, that was life at the moment in time in the place I happened to be. Occasionally people want to be photogrpahed and pose, a specific example was a delightful punk couple in Camden a couple of years ago who admired my Agfa Super Silette and posed. Mostly people don't care unless they think you've specifically singled them out. Given that in London everyone is photographed an average of 300 times per day by security cameras you'd think one more wouldn't matter, but it seems to if they think you've singled them out. So I do general street scenes, with older cameras and people are more likely to be curious about the camera than angry that I am taking photos. What does sometimes upset people is a DLSR or SLR because, I think, they fear I am going to publish and sell the photos.
As for taking photos of the homeless, it once served a purpose to educate people....but it's been done and is probably in bad taste....though I have considered doing portraits of a guy I got to know who was sleeping rough outside the train station I use every day. I decided not to, but kind of regret it. Musicians and performers I will sometimes photograph if they look interesting or have gathered a crowd and always give them a quid or two.