It seems every man and his dog has fallen for the "earn $5,000 a month for doing nothing" rubbish that any number of dodgy SEO practitioners and website content creators are sprouting.
The truth of the matter is that to make any money out of Google's Adsense, a couple of pretty basic rules apply:
1) You need good content. There's little point whacking up any old copy that just happens to be SEO'd up to the eyeballs with high paying keywords if it doesn't make sense. People are spending far too much time optimizing their copy to get high paying Adsense ads on their pages, and forgetting about actually offering something to their readers. Your readers won't come back if you provide them with no reason to.
2) You need traffic to make money from Adsense and lots of it. With average payouts somewhere between $0.10 and $0.50 for ad clicks, you need a lot of clicks to make it worthwhile. Consider this - the accepted click through rate for Adsense ads is somewhere around one percent, that's right - anyone who tells you that they're getting 10 percent is either lying to you because they're trying to sell you something, or employing dubious tactics that will probably get them banned from the Adsense program soon. With a click through rate of one percent, and, let's say, a payout of $0.25 per click, how many page views do you need to make $100 a month (the minimum monthly earnings before Google will send you an Adsense check)? Well - you're going to need 400 ad clicks ($0.25 x 400 = $100), to get those 400 ad clicks at a one percent click through rate you're going to need 40,000 page views.
3) You need buckets of original content. Taking the above example, of requiring 40,000 page views, and supposing that you have worked your ass of to produce 100 pages of quality, focused, keyword rich content, you're still going to need each of those lovingly hand crafted pages to be viewed 400 times each month to reach your goal. That's a lot of back-links and word of mouth you're going to need!
4) You need to update your content regularly. Search Engines will drop you like a stone if you don't update you site regularly. The professionals in the field are using automated means to update their sites at least daily to provide fresh content to the monsters which are the search engines. Find yourself off the front couple of pages in the search engines, and you might as well close your Adsense account - Google won't be sending you any money anytime soon.
5) Don't kid yourself that you can compete on high paying keywords. "But I've heard that there are keywords paying $25 per click" I hear you say. "So if I get the 400 clicks in the above example on my site about Mesothelioma, I'll make $5,000!" Yeah - good luck with that! Have a look at the first page in Google for the search term Mesothelioma, it's full of sites by people who know a whole lot more about search engine optimization than you or I.
6) Don't think that people are making a living from a single site. The people who are making a living from Google Adsense are doing it by using a network of sites. They have at least a dozen sites, all on different servers, with different IP's, with different domain names, using a careful and studied linking strategy to share traffic and page-rank among their various sites. Anybody making a living with Adsense is achieving over 2,000,000 page views a month. That's a lot of pages of good content. Just think - 12 sites, each updated with fresh content daily, is 360 new articles a month - at an average of 30 minutes each = six hours a day writing (let alone site maintenance etc.) It's sounding more and more like a full time job, without the security.
So, as you can see, making a living with Google's Adsense program is not quite as easy as some would have you believe. If you are after a way to make some pocket money on a site you already have, which has good content then go for it; but if you think you're going to make a living, think again!