Admission in research based Master's/Doctoral programme with a bachelor's from a low-ranked University in India
Focusing on test scores will not get you into MIT.

You need research experience — real, world-class, publication-quality, independent research experience.  A paper at a recognizable (from MIT) conference or workshop would be a big plus.  The top students from the various IITs have such experience.

You need a statement that clearly and compellingly describes your research interests, experience, and vision, with enough specific technical detail to be credible.  As an example: Describe a recent result (not just a paper title!) of your potential advisor, and suggest a credible strategy for applying or improving it.  Also, your statement should frame your ambition in terms of "doing great research", not in terms of "getting into MIT".  The top students from the various IITs write such statements.

You need recommendation letters from well-known (at MIT) academics that praise your research potential in personal, specific, and credible detail, with positive comparisons against other students from your home institution who have gone on to a top-10 PhD program.  Your recommenders must write the letters themselves; you should never even see them.  In particular, you should explicitly waive your right to see the letters later, if such a waiver is possible; most US schools offer such a waiver in their recommendation forms.  The top students from the various IITs have letters like this.

You need contacts.  Or more accurately, your recommenders need contacts.  Coming from "an unknown university" with a "low GPA", there is a serious risk that nobody will even open your application.  If one of your recommenders knows someone at MIT, either personally or professionally, ask them to send a quick email (or have a hallway conversation at a conference) saying "Hey, we have this great student Rahul Thakur who's applying to your department; you should take a look!"  Sending such an email yourself is unlikely to help.  CS professors get tons of emails from random students at unknown universities; we call it "spam".  The top students from the various IITs have these contacts.

You need some strategy.  All else being equal, it is harder to gain admission to top CS PhD programs to study AI than to study other areas.   AI seems to be the default areas for really smart, talented, qualified students who really have no idea what they want to do.  Machine learning is either a subset or a superset of AI, depending on your religion.  (Theory suffers from the same effect, to a smaller extent.)  In your case, you're probably better off emphasizing your interest in ubiquitous computing in your statement.  But remember, you need specific and credible technical detail.

Finally, you need luck.  Graduate admissions is an inherently random process; no one should apply to MIT expecting to be admitted.  Coming from an unknown university, your chances of admission are smaller than someone with exactly the same application coming from a highly-ranked school.  Aiming only for MIT is foolish; limiting yourself to top-20 departments may be foolish as well.  Don't rob yourself of opportunities!

After all, your real goal is to do great research, not to get into a top-20 program.  Right?