There are hundreds of strategies out there. you can start using free platforms, facebook, twitter, YouTube and fb groups. Everybody has a way and method that works for him.
You can use merchantwords.com to know the most profitable keywords people search for on Amazon, pick keywords that are low competitive, check Amazon to generate enough data about ebooks, titles, cover design, how many customer reviews and how many pages thay have, use better than their work to rank top with that keyword.
Advanced Strategy :
One of the most effective strategies out there, authors and witers use they Build Email list of responsive subscribers. when they have a new book they send it using email service like mailchimap or aweber. when it comes to earning passive income and generating hundreds of reviews, you have to build an audience before you launch. its powerful. its not always about writing a book, its about writing great book to make readers care about you and purchase your future stuff.
I have published a kindle EBook on Amazon, if you are interested in reading it, here is the link : Kindle publishing 2018