Send best wishes to Aunt Carol and get drunk (12)
I believe the answer is:
congratulate
'send best wishes to' is the definition.
'aunt carol and get drunk' is the wordplay.
'and' means one lot of letters go next to another.
'drunk' indicates an anagram.
'aunt'+'carol'+'get'='auntcarolget'
'auntcarolget' anagrammed gives 'CONGRATULATE'.
(Other definitions for congratulate that I've seen before include "Compliment" , "Praise (someone) for an achievement" , "Wish joy to" .)