Cities, by definition, are places where lots of people may be found. They are visible in the streets at almost every time of day. For an urban landscape photographer this can be a problem because people and their activities can easily become the focus of an image.
Little can be done to solve this problem beyond choosing a time of day when most people have gone home. Weekends and early mornings are the most obvious times when streets may be deserted, but there will always still be a few folk around.
It is difficult to give much guidance about including people in urban landscape images because each image is different and the people within the frame have a different significance. Any decision regarding the inclusion of people must therefore be made on a shot-by-shot basis. A single person walking across a bridge or along a street may well become the centre of interest of an image. If the decision is made to remove a person from an image, there are only a couple of realistic ways of doing so. The photographer can remain patient and await a moment, which may never come, when no one is in the frame. Alternatively the image can be taken several times with the person in different locations, and the duplicate images used to edit out the unwanted soul.
The other possible approach is of course to include the people as an integral part of the city streets, but try to compose images so that the human beings do not become the centre of interest. There are a number of ways of achieving this, the most obvious of which is to use a very slow shutter speed to blur human movement out of the image, or at least to render any human presence much less significant.