There’s an excellent article about what lenses to use for street photography here. The article also details various approaches for shooting on the street.
The author says that a 50 mm Canon 1.4 is a great lens for street photography. I can agree with that.
He also says set your camera to ISO 800 during daylight street photography. You won’t get noise, yet the camera will take a quick shot.
Last, he says don’t use a lens cap (get a UV protector instead) because you don’t want to be fumbling around with that when you want a fast shot.
Really, this is a great article, a must for any street photographers.by