This question is asked quite a bit - and the best general answer I can come up with is you have write about 400-500 hubs with an average of around 600 words each targeting niche keywords for things that people are desperate for - like how to remove acne, hair loss, weight loss, cancer, diabetes, etc..
Monetizing with Adsense and Amazon - with an emphasis on Adsense.
Mainly not writing about things that people could care less about - and focusing on "How To" and "What is" type hubs.
Getting laser targeted keyword phrase backlinks to your hubs.
Know this is not an all encompassing answer but hope it helps some.