Start reading the Editorials from Hindi Newspaper - Jansatta or Dainik Bhaskar or Hindustan or any reputed Hindi newspaper.
Check the PYQs of Hindi Compulsory Paper . You will get to know that out of 300 Marks, only 40 marks are from Grammar section. 260 Marks are for writing essay / translations / summary / comprehension.
For covering Hindi Grammar - Focus on
Practice writing in Hindi on any GS issues weekly.