As far as material is concerned, abundant material is available on Google or on this forum itself. You could have searched for it. Secondly, just the availability of material is not sufficient. You need guidance on the usage of material as well. For this, you need to work under a good mentor or guide. Generally, your manager or General Manager is the 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 is it 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!
Regards,
Dinesh Divekar