And to piggy back off maldives, you need search engine traffic. And you need unique but crappy content.
According to my experience adsense earnings comes with "Good Niche" , "Good Traffic" , "Good Placement"
You could write books about this. Basically you need a lot of traffic, and then you need to figure out what's the best placement for your ads, so you can make the most out of them.
Definitely you need a solid niche to earn from Adsense. If you get hands on a solid niche + search engine traffic = $$$.
Monitor on the click through rate and work on to find the best placement for your ads. That can only be achieved with high traffic flowing to your site.
seo traffic is not High quality visitors that will click your ads. Be partner with sites of your type (if you have Directory site, be partner with an other rdirectory.) this will be good for you and them. But attention! their site is can't be better than your's, and they can't be in the same category, but they can be a related site.
Not only do you need search engine traffic, but you got to make sure they are finding your site by the keywords you are focusing. Since all other traffic is worthless for adsense, you got to make sure that the people finding your site by the search engines are following your bread crumbs (keywords) if you know what I mean. I will repeat this until I'm blue in the face, because you may get a lot of answers from people who aren't making money from adsense, or who are making less than 0.50 a click. This is where picking a good niche comes into play. I got some niches that have paid me $8.00 a click. Thats not by accident. Anyway remember, Search engine traffic, plus crappy content, and like some of the others said, good search engine optimization (SEO) equals success.
Honestly, just read threads here. I applied for google yesterday night, was accepted today in the morning. Not even 6 hours apart. And for about 2 hours now I been reading threads in this section and gained alot of google ad knowledge. So my advice, just keep reading threads people make, theres alot of smart people in this section.
Thanks mate just made my day. Seriously, Kengeki is right. Two years ago i didnt knew anything about Adsense, keywords, placements, seo, linkbuilding, etc etc And 80% of what i've learned, was right here in DP foruns. The other 20%: Adsense blog. They have the basics. The basics that can put you on the right track.
Try and search for free ebooks on this subject, there are literally hundreds to thousands of them out there.
Takes time - a Niche is not essential - but quality content is. If you don't have returning users - it does not matter - because you will never generate enough traffic to make enough to overcome your marketing costs. Think first and foremost about how to make your site strong and unique - does not have to be in an ultra "high value" space for you to make money. But does have to give people a reason to come back...