Rub in the preparation, mum, to make it shine (7)
I believe the answer is:
burnish
'shine' is the definition.
(burnishing is a kind of shining)
'rub in the preparation mum' is the wordplay.
'the preparation' indicates an anagram.
'mum' becomes 'sh' (both can be used to tell someone to be quiet).
'rub'+'in'='rubin'
'rubin' is an anagram of 'burni'.
'burni'+'sh'='BURNISH'
'to make it' is the link.
This may not be right. 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" .)