Literally meaning “difference”, contrast in photography essentially means difference between light and dark tones. Divided into two types, tonal contrast and colour contrast, mastering this technique highly depends on you adjusting to the world and seeing every object as the camera would see. While on one hand, tonal contrast (mainly used for black and white pictures) highly requires you to see the world in black and white, colour contrast highly depends on having an impeccable knowledge of the colour wheel.
However, there’s of course no direct way to know which kind of picture demands what kind of contrast. Balancing contrast largely depends on the object, the kind of result you want to produce and also, your mood. One of primary roles of contrast to bring in focus on the main object along with revealing a typical mood. As for example, for producing a rather relaxing and calm result, low tonal contrast can be ideal. Whereas, to help the focal point stand out prominently, two opposite colours on the colour wheel should be balanced. Judge your contrast levels exactly as you would perceive and you’re a step away from producing an eye-grabbing awesome creation.