Author’s new “first” (8)
I believe the answer is:
novelist
'author's' is the definition.
(novelist is a kind of author)
'new first' is the wordplay.
'new' becomes 'novel' ('novel' can be similar in meaning to 'new').
'first' becomes 'ist'.
'novel'+'ist'='NOVELIST'
(Other definitions for novelist that I've seen before include "Fiction-writer" , "Eliot or Bronte" , "I've written" , "Author" , "Spark produced, perhaps" .)