The answer, at its basis, is largely what I convey in a great majority of my books about search engine optimization and online marketing. It all boils down to one simple concept: add tremendous amounts of value to the world. The more value you add, the more successful you become. Essentially, you have to do the most amount of work (initially at least) for the least return. Not the other way around.
One of the cool things about Google AdSense is that it's so easy to get set up. If you have a blog or website, you can sign up for a free Google AdSense Account. From there, Google will give you a unique code that you will paste onto your website. Google takes it from there, tracking your page views, traffic, and earnings on your behalf. There is no upkeep or maintenance to get this thing going, which makes it a no-brainer if you have a website already.