This is excellent advice Kanych! I think your recommendation to "sit as comfortably as you can" is an excellent piece of advice - I like reading on the bus or train (if I can get a good seat). I also use highlighter pens to mark the main ideas, and I write notes in the margins.
As you say, once you have picked out the main ideas, then you can start to rewrite them into your essay notes. You can also pick out some key quotations that you will cite in your essay. Remember, though, even when you are paraphrasing another author's work you should still reference it!
So, Anil, I think you're asking how to read for "gist" - this is getting the main ideas and meaning without reading deeply or thoroughly. You can actually train yourself to quickly read a text. You can start by trying to read quickly over a paragraph and then pausing to consider how much you have understood. If you think you have a reasonable understanding of what the writer is saying, you can then move to the next paragraph, and so on... You'll find that you get better at doing this the more you practise.
But, you should be aware that many academic texts use language very carefully to develop arguments and to interpret findings. So, if you read for gist, you may actually miss some of the key arguments, and the danger of this is that you will then misinterpret the text.
Remember, we read in order to learn, so you really need to make sure that you understand what you're reading. And by "understand", I mean that you think about what you're reading. Take the information in and think about it. Don't just rush through the text - it isn't a race. Read a section and sit back to digest the information. Allow your brain time to process the information. In this way you are much more likely to truly understand the subject, than if you race through the information to get to the end.