Rub in the preparation, mum, to make it shine (7)
I believe the answer is:
burnish
'shine' is the definition.
(burnish is a kind of shine)
'rub in the preparation mum' is the wordplay.
'the preparation' indicates anagramming the letters.
'mum' becomes 'sh' (I've seen this in other clues).
'rub'+'in'='rubin'
'rubin' anagrammed gives 'burni'.
'burni'+'sh'='BURNISH'
'to make it' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for burnish that I've seen before include "Make shiny by friction" , "Shine by rubbing" , "Polish to a high shine" , "Polish by rubbing" , "Make bright by rubbing" .)