Dine with Ralph, prepared to flirt (9)
I believe the answer is:
philander
'flirt' is the definition.
('philander' can be a synonym of 'flirt')
'dine with ralph prepared' is the wordplay.
'with' is a charade indicator (letters next to each other).
'prepared' indicates an anagram.
'dine'+'ralph'='dineralph'
'dineralph' is an anagram of 'PHILANDER'.
'to' acts as a link.
(Other definitions for philander that I've seen before include "Have affairs" , "Play the field" , "Womanize" , "Flirt, chase women" , "Have an affair" .)