Dear Aspirant

Important books for IBPS PO English Language Preparation are:

For good command of grammar and vocabulary

• High School English Grammar and Composition by Wren & Martin
• Word Power Made Easy by Norman Lewis

For topic-level preparation and practice

• Objective General English by SP Bakshi  (Arihant Publication)
• Mirror of Common Errors

Along with the aforementioned books, develop a habit to read a newspaper (The Economist and The Hindu are recommended). It will not only improve your vocabulary but also improve your reading speed that would benefit you during the exam.

Hope this helps