Dear Majeed,
As far as material is concerned, abundant material is available on Google or on this forum itself. You could have searched it. Secondly, just availability of material is not sufficient. You need guidance on the usage of material also. For this, you need to work under good mentor or guide. Generally your manager or General Manager is best guide. Learn from him or her.
Unfortunately, because of social media the quality of English is getting eroded. Earlier it was a matter of self-esteem to have command over English. No longer it is so.
Anyway, you may check my past reply that I had given almost seven years ago:
https://www.citehr.com/118064-how-im...on-skills.html
All the best!
Dinesh Divekar