Line up again for the true gin cocktail (7)
I believe the answer is:
realign
'line up again' is the definition.
('align' can be a synonym for 'line up' so perhaps 'realign' is OK for 'line up again')
'true gin cocktail' is the wordplay.
'true' becomes 'real' (similar in meaning).
'cocktail' indicates anagramming the letters.
'gin' is an anagram of 'ign'.
'real'+'ign'='REALIGN'
'for the' acts as a link.
(Other definitions for realign that I've seen before include "new dressing" , "Group or divide on a new basis" , "Change position (of something)" , "Set straight" , "Make new alliances" .)