I want to start a ratings and reviews website that rates the best trainers in India across various areas like soft skills training, programming, financial modeling, etc.
In the long term you want people to add themselves, or be added by others to your website. However, to start things off you're going to have to do a lot of work yourself to seed the site with people yourself.
1) Go to existing institutes where those things are taught (programming, financial modeling, etc.) and ask the students coming out the door how they would rate their instructors. These institutes might be tutoring agencies for standardized tests, etc.
2) Professors at universities might be interested in teaching / tutoring on the side, so ask university students to rate their professors.
3) Then go to all of the instructors that you have the names of, and ask them if they know anyone else that they think might like to be added to your site. Find where those people work, and keep expanding.
Once you've got a big enough seed of people that you've added, start spreading the word. Put up fliers at universities, post on internet forums, etc.
Note: It might be best to initially start with a more well defined type of instructor. For instance, maybe only programming instructors. Choose the one category that there would be most demand for. This will help you during your initial stages because you'll be able to better learn everything about where they hang out, how to get them to contribute to your website, etc. Once you've got that initial core group you can slowly start expanding out to all types of instructors.
Let me know if you'd like more specific advice relative to the specifics of your idea,
I have over 12 years of experience in building directory websites similar to yelp. There are many php scripts or Wordpress directory themes available which can help you create a MVP. Each niche has some specific requirements. As a first step, we need to set up a meeting to discuss the requirement in detail.