You can believe one of two things about making a significant income from Google AdSense.
1) If you believe the claims of those who are promoting AdSense with the products they are selling, then Google AdSense is the key to your early, as in nest year, retirement.
2) If you believe those who have spent the past year working with AdSense and received something in the neighborhood of $100 for their efforts, you will begin devising an alternative retirement strategy.
But is there a middle ground, a third option which will allow you to make a reasonable income from Google Adsense in return for a reasonable amount of works? There certainly is, if you don't keep looking for the magic tricks and resign yourself to repeating the same R&D over and over again.
Keywords are at the heart of any successful Google AdSense campaign, and you need to find the right ones. The right keywords will be determined by your source of traffic.
If you intend to use natural SEO, then your will need to get and Adwords account and use it to research the keywords with good PPC value, good bidder density, and not many competitors.
Any keywords which can supply you with all three are the ones on which you should build your niche, so use them to build a search engine optimized site, post your AdSense ads, and start looking for your traffic to arrive.
Then do it again, and again, and again, until you have enough sites built on enough smartly chosen keywords to make AdSense pay off for you.
There's one more way to build respectable revenue from Google AdSense. It's called arbitrage, and what it means is that you will buy PPC traffic directly from Google via AdWords, and then steer that traffic to your site displaying AdSense ads.
If you want to engage in arbitrage, look for high PPG value keyword for your websites, and low PPC costs for your ads.
While either of these strategies, if implemented correctly, can generate a reasonable and ongoing income from Google AdSense, the real keyword is patience: you'll almost certainly have to wait months before you see your first AdSense checks.
If done properly, either of these techniques can yield a consistent income, but more than likely, it will take months before this occurs.