Ramil, if you like science fiction, start reading Frank Herbert's "Dune" series. Great set of books, well-written, and very good grammar. Stephen King also. I think your level of English is good, and these books are fun to read. These are written in American English. For a British style, then I'd recommend The Harry Potter series. Very well-written, and I learned many British vocabulary words that we never use in America.
For something more literary... try reading anything from William Faulkner, Thomas Pynchon, and Mark Helprin. Helprin's
Winter's Tale is well-written, the grammar is excellent, and it's a fun read. American English.
The Lord of the Rings. Tolkien was an English linguist and professor, and these books are written in excellent grammar. British English.
James Joyce's
Ulysses. "Joyce" English. Unlike any other English, except perhaps William Faulkner. Joyce was Irish.
William Faulkner's
The Sound and the Fury. "Faulkner" English. Faulkner was a Southern American. Very southern!
Joyce and Faulkner are widely considered to be the two best English authors of the 20th century. Yet, they threw "correct" grammar away, and developed their own styles and grammar... called "stream of consciousness". Pure English, their books are considered
classics... and yet they broke all the grammar rules. But their books are masterpieces.
Thomas Pynchon's
Gravity's Rainbow,
Crying of Lot 49, and his others (he's still alive and writing), has developed his own style of English, and also breaks many grammar rules, in a very brilliant and wonderful way. He's probably the best living American author. He is of Joyce and Faulkner.