Taking portrait photos can be an enriching experience for both you and the subject of the photo. Since this is the age of the selfie, one can see how this type of photography is being taken for granted. This does not mean that you have to abandon it if you find that you have an interest. These are some advice I can give you from my own experience.
Respect Peoples Intimacy
One can find himself in a situation where he can make a good portrait of someone, but the photo can insult the person. Especially if it is interrupting an intimate moment that person is having. This is why you should always ask for permission, and if the person asks you to delete the photo respect their wish.
When you try to take a photo of people while they are doing something, try not to be noticed. People can often change their expression or posture when they know someone is looking at them through the objective. This is why you should try to be as unobtrusive as possible.
Observe Human Behavior
A major part of portrait photography is knowing your subject sufficiently enough so you can predict what they are going to do. This is the only way you can capture what you want at the right moment. Watch people carefully and always have your camera ready. Prepare the device for the situation you are shooting, so you don’t have to do it while your subjects are moving, you can miss out on great opportunities that way.
Engage Different People and Cultures
Approach the people you want to take photos of and get to know them. Make them feel comfortable with your camera’s objective. Maybe you can discover something about them, that can help you in capturing their essence in a better way. Don’t rush into a situation with your camera blazing, maybe even leave it in the bag and take it out when you feel that the situation is right.
On the other hand, if you are interested in capturing cultures that are different than your own then you need some research before going into the field. Talk to people who have been there and find out if there are any taboos in public photography. And learn some phrases in the local language. Respect the culture you are visiting, and the beliefs of the local people. That way you will have their respect in return and that could give you an opportunity to make a great photo.