Dreadful writer goes in for rich novel (8)
I believe the answer is:
horrific
'dreadful' is the definition.
('horrific' can be a synonym of 'dreadful')
'writer goes in for rich novel' is the wordplay.
'writer' becomes 'i' (the person who is writing these clues).
'goes in' means one lot of letters goes inside another.
'novel' is an anagram indicator.
'for'+'rich'='forrich'
'forrich' anagrammed gives 'horrfic'.
'i' going into 'horrfic' is 'HORRIFIC'.
(Other definitions for horrific that I've seen before include "Causing fear" , "Dire" , "Appalling" , "Arousing feelings of shock and fear" , "Ghastly, shocking" .)