Render song about maiden I left looking happy (7)
I believe the answer is:
smiling
'looking happy' is the definition.
'render song about maiden i left' is the wordplay.
'render song' becomes 'sing'.
'about' means one lot of letters goes inside another.
'maiden' becomes 'm' (cricket abbreviation).
'left' becomes 'l' (common abbreviation).
'm'+'i'+'l'='mil'
'sing' enclosing 'mil' is 'SMILING'.
(Other definitions for smiling that I've seen before include "Visibly amused" , "Slowing word to horse" , "Beaming, grinning" .)