First, you need to get rid of distractions. For most people, they cannot stay calm or concentrate well because they are distracted by something. Every human has five senses: sight, sound, smell, touch and taste. Make sure you are not distracted by any one of these senses.
Most people have a problem with being distracted by noise. If you hear loud noises going off everywhere, buy a good set of headphones. The best solution is to isolate yourself in a quiet setting.
Escaping into fantasy is another way to keep the mind calm. Think about calm things, objects and settings. Some people like to look at paintings or photographs of nature. Other people like to think of a non-concrete object, such as color or movement. They like to look at abstract art pieces that do not focus on reality at all. That way, you will definitely make your mind calm.