No doubt, I am a writer, but can someone give me some tips to be a better writer. I want to write stories like O Henry, Muppassant, Edgar Ellan Poe and Sadat Hasan Manto. But whenever I start writing, I can't invent plots. How to invent plots like great story tellers of the world? Please someone guide me.

I don't think writing is about plots per se. It's the message or meaning or concept behind the plot. The plot is merely a vehicle for something thought provoking.
Unless you want to write pulp fiction. Which sells very well!

Some famous writers say 'Write what you know about.' Other famous writers say 'Please don't - there's nothing more boring. Learn how to invent.'

It really doesn't matter what anyone tells you, because you will find within you the method, style, and reasons for writing that compel you to write.

What's a book you've read recently that impressed you? One novel I like is Life of Pi, Pi being an Indian boy adrift at sea in a lifeboat with some zoo animals, a mysteriously allegorical novel with some interesting turns in the plot. I don't want answers to philosophical questions necessarily! It's a book that was rejected at first by many publishers, but won many awards after finally getting accepted.

But I also like all the Girl With the Dragon Tattoo novels, which are pretty bluntly about a tough young woman fighting back against sexual discrimination and abuse. They are action packed and sold millions and were made into movies.