Tutor sat prepared to begin (5,3)
I believe the answer is:
start out
'begin' is the definition.
('start out' can be a synonym of 'begin')
'tutor sat prepared' is the wordplay.
'prepared' is an anagram indicator.
'tutor'+'sat'='tutorsat'
'tutorsat' is an anagram of 'START OUT'.
'to' acts as a link.
(Other definitions for start out that I've seen before include "hit the road" , "Take off" , "Begin a journey" , "Embark (on a venture)" , "launch" .)