Pick out suit with shindig having been arranged (11)
I believe the answer is:
distinguish
'pick out' is the definition.
(I know that pick out can be written as distinguish)
'suit with shindig having been arranged' is the wordplay.
'with' means one lot of letters go next to another.
'having been arranged' indicates anagramming the letters.
'suit'+'shindig'='suitshindig'
'suitshindig' anagrammed gives 'DISTINGUISH'.
(Other definitions for distinguish that I've seen before include "Make out" , "discriminate" , "Differentiate" .)