Hi Kunal! For Verbal Ability, it is best to go by the basics. The first and foremost study material you should refer to is the English Grammar text book, or Wren & Martin. It is best to start with practice. Solve the worksheets or past years' questions. Apart from that, Word Power Made by Norman Lewis is another good book to build vocabulary. Some other comprehensive books for Verbal Ability are as follows:

• Objective General English by SP Bakshi (Arihant Publishers)
• Quick Learning Objective General English by RS Aggarwal