Bang on about one’s spruce clothes (endlessly) (7)
I believe the answer is:
precise
'bang on' is the definition.
'about one's spruce clothes endlessly' is the wordplay.
I cannot quite see how this works, but
'about' could be 're' ('re' means regarding or about) and 're' is found within the answer.
'one's' could be 'is' (Roman numeral) and 'is' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for precise that I've seen before include "'Exact, accurate (7)'" , "Specific" , "Highly accurate and sharply exact" , "Detailed, exact" , "with accuracy" .)