Polish ruse uncovered in instructions (6)
I believe the answer is:
rubric
'instructions' is the definition.
(I've seen this before)
'polish ruse uncovered' is the wordplay.
'polish' becomes 'rub' (polish meaning rub to make shiny).
'ruse' becomes 'trick' (I've seen this in another clue).
'uncovered' means to look at the middle letters.
The central letters of 'trick' are 'ric'.
'rub'+'ric'='RUBRIC'
'in' is the link.
(Other definitions for rubric that I've seen before include "Title or heading or instruction printed in a special type" , "Directions for the conduct of Christian services" , "Service-conduct instruction" , "Written instructions" , "set of instructions" .)