First and foremost you got to have quality contents that can engage visitors. You have to be consistent with your content production and publishing. Then you've got to have some in depth knowledge of SEO. If you are not a natural writer and doesn't enjoy it, then this thing is not gonna work. Even if you are able to produce good enough stuff regularly, if your SEO skills are not good enough, then you are not going to make anything worth for the time you've invested in researching and writing stuff. By my experience it didn't go well for me after years of failed attempts. Anyways if you want to give it a try, you should learn the hard way. This is not to discourage. But its the harsh reality. Lastly if you've made up your mind to give it a go, then remember to write contents and plan your SEO targeting countries that have good pay rates. Otherwise its not worth the effort. However contents sites are not the only way to generate traffic and display ads.