The General Assembly may be convened at any time by any shareholder holding a certain portion of the share capital and notably on all questions listed in the bylaws as requiring a collective agreement.
Generally, it is the CEO who convenes the other shareholders to vote on important decisions or those listed in the bylaws and submitted to a vote.
All this information depends on the content of your bylaws.
The documents proposed by madeinlaw.com include short notice periods, flexible terms of reference and conditions for majorities enabling managers to make the majority of management decisions independently. Only the Extraordinary General Assembly is hold for the most important decisions such as a change in the company's nationality for example.