For travel photographers, being out and about in unknown urban settings mainly means taking postcard-style pictures of streets, narrow alleyways, squares, promenades and sights. It takes a certain amount of strength to overcome your natural reticence about taking pictures of strangers in specific street scenes. If you are out and about with a small, unassuming compact camera, you are less likely to encounter resistance than if you have all the professional kit. In principle, taking pictures of people without their consent should be considered 'not allowed' as everyone has the right to their own image. However, in many aspects of public life on the streets, it is not practical to ask everyone if they mind you taking pictures. That said, of course, I strongly recommend that you do exactly this. If you approach people directly and chat to them, they are often more open than you think. Taking pictures of people is less of an issue in the amateur domain where there is no commercial use. But if you are posting on social media, you need to be very careful and expect to be asked to take a picture down. It's no big deal. When it comes to making a decision, I say: take the picture! You can always delete the picture if someone asks.
And surprised faces can make for the most expressive images. I recommend a zoom lens with a focal length of around 24-80 mm for this. Hold the camera ready in your hand and use automatic mode (P) or timer (S or T). Make sure the shutter speed is 1/125 seconds or lower so the pictures do not get blurred.
It is very difficult to plan street photography, as situations emerge all the time as you wander through a city or a district. But concentrate on the people rather than the sights. If possible, do not take pictures from behind, since rear views are not nearly as interesting as faces. If you cannot muster up the courage to just take pictures, then ask people whether they mind. If you are polite and friendly as a tourist, lots of people will allow you to take their picture without any stress. And the worst that will happen is that someone will say no.