I am a government school student2020 now . I wish to join genetic engineering. all the entrance questions will be in English. I am tamil medium student. so , how can i prepare for this entrance. please reply me

Rajiv, NTA did mention that they will conduct JEE Maina in 11 regional languages from 2021. So it might actually help you. But yes JEE Mains is not the only Entrance examination so improving the command over English is the way for now. We have few books to recommend and few tips for you:

Word Power Made Easy (by Norman Lewis)
This is the go-to book to improve your vocabulary. It is not a book to be read but a book to work with daily to enrich your vocabulary.

High School Grammar and Composition( by Wren and Martin)
It is a very good book for people who want to improve their grammar skills. It helps to understand and conceptualise different aspects of grammar and it is a must have book for anyone with poor grasp on verbal ability or who wants to make up with the basics of english.

Read books from different genres
The ultimate key to improve your verbal ability is to read extensively and to read books from different genres. This ensures that when the time for reading comprehension comes you are well acquainted with different writing styles and topics. Reading extensively also improves your reading speeding over a period of time. There are no shortcuts here.