If you are uncomfortable with this type of photography a long lens allows distance between the subjects and you and gives you that comfort zone to work in. I have taken many a “candid” photograph both at close up and far distances from the subject. The thing that I find is surprisingly that most people are more shocked that you are and will usually just carry on with what they were doing even if they spot you taking their picture. You would be surprised how many people are actually flattered by you wanting to take their photograph, if you approach them and are confident but polite they behave remarkably well and most will even pose if you want them to.
The law basically says that anyone is fair game in a public place. I usually apply common sense and to date have only had one altercation with the police. I was with a friend in the centre of Manchester where there is a water feature that consists of many, many separate water jets that randomly shoot up into the air. This is right in the city centre and on public property. During the summer many children are taken there with parents to splash and play in the water offering some great photo opportunities. We had been there for about 40 mins when we where approached by a lone policeman, he said that there had been complaints made about us and asked what we were doing. I told him that we where both amateur photographers and were taking photographs intended for a competition. He tried to get heavy with us until I made it clear to him that I knew we where not breaking any laws and that we were on public property, I offered to show him the photographs (which were mainly of kids smiling faces and throwing water about) but he was not interested. He agreed that we were not breaking any laws but didn’t want to have to sort out any hassle if any of the parents should decide to stop us taking photos themselves. The conversation continued for a short while but in the end we just moved on to save the hassle. The moral??? Know the law I suppose, and be prepared to retreat to save trouble even if you know you are right.
A good place to learn people photography is the car and bike shows. Many of the companies hire pretty girls to promote their products and they are paid to look pretty and be friendly. They will happily pose for you and most of the time they are used to being in front of the camera. Nice smiles and good poses are usually given without any or with virtually no guidance. The only problem with this is once you have started to get a few shots you will find many other “men” also jostling for their attention. One minute they are all yours and the next you have an audience. Its all part of the fun.