Hey,

See to become an expert in English, not always textbooks will help . Try to read story books, magazines, newspapers also listen songs and podcasts in English. It will help you to  learn new words, also it will enhance your vocabulary too.

If you need to improve your grammar and other things then l am providing you a list below you can refer.

1. Essential English Grammar by Raymond Murphy
2. Intermediate English Grammar by Raymond Murphy
3. The Penguin Writer’s Manual by Martin Manser and Stephen Curtis
4. The Elements of Style by Strunk & White
5. On Writing Well by William Zinsser
6. All about Words by Maxwell Nurnberg and Morris Rosenblum
7. How to Build a Better Vocabulary by Maxwell Nurnberg and Morris Rosenblum

Hope it helps.

If you need any particular suggestion then feel free to comment below.

Thank You.