Technically people pictures are better if the background is in soft focus. You can achieve this by shooting with an open aperture (lesson ("aperture"). lighting can be of secondary importance, better to have a face with great character badly lit, than one well lit but expressionless.
Photographing people in the street can be problematical if they think their privacy is being invaded, particularly if you don't speak their language. There are two ways of approaching this situation, the paparazzi way, or the polite way.
When going abroad learn the word for "hello". In far-flung places like Tibet they will appreciate your courtesy and allow you to photograph them. This sometimes means missing that natural look, in which case return after 5 or 10 minutes hide with a long lens and shoot them again when they are not posed and behaving naturally. After a couple of minutes of shooting let them see you again, they think you're playing a game with them and start laughing. Keep shooting and you have the serious, the candid and the relaxed smiling shots, all in one go.
I would advise anyone if your subject says no, then leave it at that, it's not worth the problems you might cause people photography can lead to difficult situations..
Sometimes a little money or a cigarette can help when shooting people in the street, even if you don't smoke carry a packet in your camera bag. In Tibet a photo of the Dahli Lama helps but be careful, as when I was there it was illegal to carry one.
Whe photographing people In under developed countries the kids love chocolates, sweets, ballpoint pens, or cheap T-shirts, but again be careful, when you treat one, his mates might find out and you’ll be surrounded by screaming kids!
My way out of this was to give the biggest in the group the responsibility to keep the others out my way, however It didn't allways work as you can see above.
While candid shots are great don't worry if your subject looks directly into the lens, it gives the Morrocan above , a menacing and challenging look.
I hope this has given you confidence to go out on the street and start photographing people.