It is easy to take good pictures, difficult to take very good pictures, and almost impossible to take great pictures.
By that reckoning Henri Cartier-Bresson is the greatest photographer of the 20th century – who else has truly great photographs falling out of their closet? And if you’re a photographer one of the ways you become a better photographer and come to understand your artistic practice in deeper ways is to hang out with other artists, preferably artists who are ahead of you. And Henri C-B is ahead of everyone. So seeing as Henri died in 2004 the best I can do is refer you to this interview.