If it is about writing answers to questions then he should read the lesson thoroughly so that he is able to find the answer quickly. Also it will help him in understanding lesson. If there is problem in grammar then he should practice grammar exercises. In the beginning he'llmake mistakes but slowly and steadily he'll be perfect in grammar. Also ask him to read dictionary on regular basis to enhance his vocabulary. He should read English newspapers so that he'll come across new words. If it is about the writing section then he should prefer writing more and more by himself like articles, speech, e-mail, letters etc. .Also he should prefer watching English channels as this will help in enriching his listening skills as well as speaking skills ( speaking English.) This will help him in both i.e. in his homework and in the enhancement of his English.