Founder of SEO & CRO agencies in Paris - Proud owner of digital ventures delivering value since 2005 .: leanstartup + business model generation addict, traffic generation & monetization :.
Find a niche / subject that you love (you'll have to write a lot) and develop content around common problems in the niche. Try to monetize these first articles using adsense and product reviews to validate the niche and your angle (around 60 articles).
You can use guest posting to build your domain authority during this first phase.
There are many ways to bootstrap an authority website / affiliate website but this is the one i've used in the past. As soon as your website can finance content creation it'll scale quickly.
Hope it'll help.