Soon favourites must return for a light-hearted dance (9)
I believe the answer is:
quickstep
'light-hearted dance' is the definition.
'quickstep' can be an answer for 'dance' (quickstep is a kind of dance). I am not sure about the 'light-hearted' bit.
'soon favourites must return' is the wordplay.
'soon' becomes 'quick' (I am not sure about this - if you are sure you should believe this answer much more).
'favourites' becomes 'pets' ('pet' can be a synonym of 'favourite').
'must return' says the letters should be written backwards.
'pets' reversed gives 'step'.
'quick'+'step'='QUICKSTEP'
'for a' acts as a link.
Can you help me to learn more?
(Other definitions for quickstep that I've seen before include "Fast dance" , "Fast foxtrot" , "Modern ballroom dance" , "Lively dance" , "dance music" .)