What did a greek philosophers believe was most important in life?

Answer that I'll offer:  PURSUING WISDOM

There were many Greek philosophers, and their ideas were not all in agreement with each other.  But in general, the Greek philosophers all agreed that pursuing wisdom is the most important thing in life.  One of the earliest of Greek philosophers, Pythagoras (in the 6th century BC), is thought to have coined the term "philosopher."  The report is that Pythagoras did not want to claim to be a wise man who already had great wisdom, but that he was a "lover of wisdom" who sought to be wise.  In Greek, "philos" is a word for "love" and "sophia" is the word for wisdom.  So a "philosopher" is a "lover of wisdom."

The great philosopher Socrates (5th century BC) was famous for saying, "The unexamined life is not worth living."  He saw the goal of his life as constantly seeking wisdom -- and that what truly made him wise was recognizing how little he truly knew with certainty.

Other Greek philosophers like Plato and Aristotle and more followed in that tradition.  They did not all agree on all the details of what the best pattern is for life in this world.  But they did all seek wisdom as the most important thing in life.