Orderly sorting out messy attic (10)
I believe the answer is:
systematic
'orderly' is the definition.
(synonyms)
'sorting out messy attic' is the wordplay.
'sorting out' is an anagram indicator.
'messy'+'attic'='messyattic'
'messyattic' with letters rearranged gives 'SYSTEMATIC'.
(Other definitions for systematic that I've seen before include "Methodical" , "Done methodically" , "intentional" , "organised" , "Structured" .)