Sober singer steals heart of merry groom (5)
I believe the answer is:
prink
'groom' is the definition.
(prink can mean to groom or tidy oneself)
'sober singer steals heart of merry' is the wordplay.
'sober singer steals' becomes 'pri' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'heart of' says to take the centre.
'merry' becomes 'spanking' (synonyms).
The central letters of 'spanking' are 'nk'.
'pri'+'nk'='PRINK'
Can you help me to learn more?
(Other definitions for prink that I've seen before include "Smarten" , "Deck out" , "Preen, dress finely" , "Make minor changes to one's appearance" .)