Tidiest head of art involved in north-east exam (7)
I believe the answer is:
neatest
'tidiest' is the definition.
('neat' can be a synonym of 'tidy')
'head of art involved in north-east exam' is the wordplay.
'head of' says to take the initial letters.
'involved in' means one lot of letters goes inside another.
'north east' becomes 'ne'.
'exam' becomes 'test' (synonyms).
The initial letter of 'art' is 'a'.
'ne'+'test'='netest'
'a' placed into 'netest' is 'NEATEST'.
(Other definitions for neatest that I've seen before include "Most orderly" , "Most smart" , "best-looking desk, say?" , "Most tidy" , "Seat ten (anag)" .)