Human brains are formed to be allured by rhythm. It can be a rhythm afforded by symmetry, balance or repetition. The form can be music, calligraphy or photography, you name it.
In a stricter visual sense, rhythm is the interlacing of regular elements in an image, namely, the dots, lines and planes.
By saying dots, lines and sections, we don't take the literal meaning. Take the photos here for example. The dots can be the heads of the passers-by as seen from an aerial angle. The lines can be the taxi or van queues. And each picture of the model on the billboard can be taken as the planes.
Rhythm exists in everyday scenes. Go to the street and take notice of the vehicles whizzing past and passers-by going up or down the road in different paces. Admire the skylines formed by the buildings of varied heights. Go to the countryside and see the labyrinthic paths and the winding curves of fields and rivers. All these can bestow a sense of rhythm on an image.
You may read books about how the specific kind of elements can give theoretically what an impression to the viewers. But the best and easier way is to first figure it out yourselves by going out with your camera, observing with your heart and taking photos.
Practise, practise and practise.