When it comes to promoting your self-published book, traditional book marketing strategies can still be highly effective. But if you want to reach a wider audience and get connected to more potential readers, the solution is social media marketing.
With social media, you don't have to waste your money on paid advertising in print, radio, or TV media; you don't have to exert a bunch of energy planning readings or book tours; and you don't have to spend time trying to impress a bunch of book critics. All you need to do is create a connection to other people. That's the purpose of social media, after all.
I'm not saying that traditional marketing doesn't work anymore, because it occasionally still can. It's just that it doesn't guarantee that your book will sell a million copies or become a success — and it costs a lot of money. Social media, on the other hand, is free.