How the manager should behave with his staff to be a good manager or team leader? should he be friendly with them or strict?

This highly depends on the manager/team leader personality and his/her assessment of the employee.situation he.she is dealing with.  It also depends on the "management style" and "corporate culture: of the organization itself. Being "friendly" doesn not necessarily means  being "soft" with the employees/situation where strictness is needed.   As a manager, I can be very friendly and blunt about things/people when they go wrong.    I also need to be clear and honest and prompt when dealing with these situations to stop things from accumulating and deteriorating. 

I believe a manager/team leader should be "crystal clear",  "honest" and "fair" when dealing with these situations, and I am sure with no hidden agendas influencing managers attitude/aqctions, it will all be appreciated by the employees !

50/50 according to each situation

An effective manager should build trust within his/her work environment. He/she should use the most suitable tools and techniques for the case in hand. Being friendly is better for some cases while being strict is better for others.

He should be friendly outside the office but during work he should be strict to a level that his sub ordinate can bear.