Normally, I like to start with a process (includes more than one department) that rapidly brings performance improvements. For example, for a manufacturing company, starting with a process like “Supply materials” (evaluate and qualify suppliers, order materials, receive and control materials, store materials, supply materials), may bring more confidence, more control, and show measurable gains.
Sometimes I have the opportunity to start with top management clauses and processes. Normally, when top management is really committed to the management system.
what the scope should cover?
There is no technical answer to this question.
Deciding on the scope of a quality management system (QMS) is a management decision. For example, a hotel:
A hotel may develop a QMS just for the hospitality part, and just for travel agencies, not for treating individual guests.