Firstly, those 45 degree mirrors that slap on the end of lenses do work really well, i've only seen them used but you can get the most direct candid photo's because you are pointing a completely different way, i'm not sure what would happen if they noticed it and realised what was going on tho (to me anyway it's quite obvious what it's doing), might get interesting.
Ok so you don't HAVE to stick to lenses under 35mm, for instance the nifty fifty (50mm f1.8) was my first street lens, very nice and very common. Of course the 20mm F1.7 is 40mm and I find is a perfect balance, sometimes I do wish for wider though, but THERE ARE NO RULES, how can there be in something that is meant to be creative, what people state as rules are really just guidelines for what has worked in the past. I think it's all about creativity, and the more you shoot the better you get at it and more comfortable you get. I never ask permission, to me that would destroy the photo, it'a all about body language, if you feel like you can be there taking the photo it will come across that way. I've had a few evil stares, one street musician asked not to be photographed, I obliged, but that's all i've had in 2 years. There was a really good series on street photography I saw a while back which showed pro's doing it (can't remember what it was, it wasn't on youtube though

), they got amazingly close and even on the ground and framed people, nobody seemed to notice! I must find this video again and post it!!
You learn what you can and can't take, it's feeling the flow of the city (or town I suppose). This only came with time for me, now there's a feeling for what I can take and it gets easier and easier, and a lot of are just straight up photo's of people right infront of me.
Few tips:
- If you notice a fairly static scene, take photo's of things around it first, then of it directly (I liked the tip about pretending to take a video, different take on it)
- If you're taking a photo of someone fairly close and direct, after taking it, stare passed them like you're interested in what's behind them, don't make eye contact unless it feels like they're staring at you (like how you'd look at anyone staring at you), then just smile, you're allowed, i'm respectful if they approach but they never seem to.
- Walk slowly, all your motions should be fairly slow, slower than the general pace of the crowd around you, don't suddenly jerk the camera to your eye, look "considered and relaxed".
- As composition general goes, you're not often framing the subject directly in the middle, therefore focus on something in the same plane (ground even) and look like you're shooting past them.
- Occasionally if it's a difficult shot i'll pretend to be frustrated with my camera, like it isn't working properly, checking things and pressing buttons, inspecting it closely and taking "test shots", people can notice you this way but they generally never say or do anything because it kinda makes sense.
- Keep your arms in and at your side, you should only really see the outline of your torso, it reduces your impact significantly, I only noticed this after seeing my shadow in some shots with my arms out wide

- I could go on and on but the main thing is, public life is your canvas, you aren't a pervert, you aren't a criminal, you're doing nothing wrong and in fact if you get really good you are doing a service to the place, you've got to exude this confidence. Some days it just doesn't feel right you're in the wrong frame of mind and that's fine, some days it feels great, trust your intuition.
I love good street photo's, there are a lot of bad street photo's about, every 6 months or so I start to hate my old stuff because I feel i've progressed, try to have a critical eye and not just snap random strangers doing nothing, frame things like actual photo's, shoot from the hip but realise you'll get about 1 in 100 from this, sometimes it's the only way though, there is always luck involved anyway. Have fun!!
Oh and don't be afraid to leave your ISO on 400 even in good light (unless clipping the max SS), and did I mention shoot in aperture or shutter priority.