Testing and checking the regulator and the tank for leaks should also be practiced. Mobility is trained, using your body and your buoyancy control. Buddy breathing and life jacket technique is essential for the safety of the diver. Rescue and first aid are also good things to know. Even basic training is very important in diving, as it is a potentially dangerous sport.
All skills have to be maintained while learning new ones.
A diver, however experienced, is never fully trained. There are several diving organizations, but there are two which stand out as recognized throughout the whole world and more or less dominate the world of diving. PADI is the other organization with 'Open Water' and 'Advanced Open Water' certificates. The PADI Open Water certificate is equivalent to CMAS First Star. To dive, the diver needs his certificate, a logbook with a record of his previous dives, and a valid medical examination.