The best way to promote bitcoin is explain to a friend who are willing to earn bitcoins.
Promotion these days hits the only point of using social media. Fb, Twitter, Instagram, Pinterest, snap chat etc are social media platforms where one can put up ads and posts to promote Bitcoin.
Facebook is banning all ads that promote cryptocurrencies, including bitcoin, in an effort to prevent people from advertising what the company is calling financial products and services frequently associated with misleading or deceptive promotional practices.