Could you Please recommend me interesting non-technical books i could read which will help me improve my writing skills?
The easiest way to improve your writing skills is to read, and read a lot. The best writers are also avid readers. Reading helps you learn grammar, vocabulary, sentence structure, world building, characterization, and so much more. You should read as many books as you can - both good books and bad.
By reading good books you're able to see what works. You'll see deep characters and learn techniques to make your own characters deep. You'll learn how to write well and keep your readers engaged.
By reading bad books, you'll learn what doesn't work. You'll see what flat characters are like. You'll learn what loses a readers attention and what confuses them. You'll see bad grammar and sentence structure.
The basic message: Read. A lot. Whatever you can get your hands on. Whether you read a book a day or a book a week, just read.
If you are looking at how-to books, both Stephen King and Orson Scott Card have some excellent books on the subject. Don't be put off by their genres.
Reading is very important, but don't ever forget to spend time doing deliberate practice writing. Do short pieces that focus on setting, descriptions, dialog, &etc. Set limits like 100/10,000 words, or imitate someone who has a distinctive style like Tom Clancy.
I'm not sure whether you're looking for how-to-write books or just books in general. Based on your writing in this short question, I'm going to say that I think it's a bit early for how-to books, and recommend that you just read a lot of anything you can find in English and work on getting the general vibe down. After you've done that for a while, it may be time to start writing and working on refinement.
If you feel that you're already at the point for how-to books, it would help if you'd let us know what type of writing you want to do. The rules are different depending on whether you're writing fiction or non-fiction, etc.
The Elements of Style by William Strunk Jr. and E.B. White.
Read anything by Orwell, anything Nabokov. If you like something just a little down-market from there, Martin Cruz Smith and Scott Turow both write thrillers but with lovely use of language and characterization.
It doesn't matter how ridiculous a lie is if it's your only chance of escape. It doesn't matter how obvious the truth is if the truth is that you'll never escape. -- Martin Cruz Smith, Gorky Park
When I read some interesting passage in a book, I'll sometimes pull out the notepad and copy it down. Gives my fingers good habits.
Also, writing longhand on plain paper makes it seem too informal to matter much so the self-critic is dismissive and I can write more freely.
In addition to reading voraciously as has already been suggested (especially, but not only, in the genre/field you want to write) you might want to check out Stein on Writing by Sol Stein. It's the best book I've seen that discusses the writing craft, and contains sections on both fiction and non-fiction.