Ok, today I review a lesson I'm trying to learn.
With strangers...make eye contact, talk to them, get permission to shoot them.
It is more polite. More importantly, it's a lot more gratifying.
Candid photography has a big role but it is all to easy to shoot from afar, voyeur-like with a long lens. See my lower shot.
The upper shot is my 12-24mm at 18mm. The other shot is an ancient Nikkor AI 105mm 2.5.
I find it so very much more satisfying to enter into a few-seconds-long implied social contract of sorts with people when they allow you to shoot their photograph.
If they seem even remotely displeased...move on.

D2X 12-24mm f/5.0 1/80th at 18mm
D2X 105mm 2.5 MF 1/125th f/2.5
One post-script: I'm bad-mouthing tele-candid photography. That is a bit ironic because I just, today, bought the 105mm f/2.5 which, in the used shop on a test pattern was absolutely amazingly sharp. Drasticly sharper that the Nikkor 24-120mm I tested it against...and even a hair sharper than my beloved Nikkor 85mm f/1.4. All the more amazing considering it's from the mid 70's, minty and a titch over a hundred bucks cheap! It still ad the little oval Japaneese sticker on it that I miss seeing.