During the last 5 months, one of the most read articles I wrote was "TB Test for UK Visa: Finding IOM." The article was published on 25th July. In about 3 months, it has earned me $1.92. Here is a graph on page views for this particular article.
As you can see, I have been getting around 18 page views a day for this particular page, and the earning have averaged at $0.024 per day. At this rate, I could be a millionaire in 114,000 years :) by just having written this single article. Or another way could be to write 10,000 such articles and become a millionaire in 11 years :) Of course, I don't have enough competition on this particular piece of information, and the information itself can get outdated easily.
On a more serious note, it's pretty obvious more traffic means more revenue. If you are looking for a single important way to increase your revenue, nothing comes closer to the effect of increasing your page views. Below are some tips in general:
Page vs SiteThe basic unit of ranking in a search engine is a page. That's true for adsense as well. If you add one good webpage on your website even that can earn you significant revenue. Strange but true: the relevance and quality of the whole site is not that important.
Difference in EarningsThe revenue per click has varied from $0.01 to $0.96. The factors that contribute to the revenue generated by a single click include:
Competitiveness of the keywordForex related advertiser might be willing to spend more on the ads than, say, an offshore textile factory. Thus, some keywords are more high paying than others. Since adsense serves ads "related" to the keywords on your webpage, it might make sense to use better-paying-keywords more often. However, this is not about writing content targeted towards a keyword, rather tweaking your content to "highlight" the right keywords you already have.
Location of your visitorA visitor from a developing country might earn you just $0.01 by clicking your ad. A similar click could earn you $1 if he/ she was from the developed world (alas! the world is broken; somebody, please fix it!)
Ads PlacementIt matters a lot how and where you put your ads. They shouldn't be too distractive. At the same time, you don’t want them to be completely hidden. Many people suggest that you experiment with different ad sizes and placements. While this is a good approach, I usually just find it enough when I think how attractive ads on other websites are.
Adsense FailsSometimes, the "matching" mechanism of Google will fail. Technology can only get you that far. For example, if your web page is about UK "pounds" (exchange rate, inflation, etc.), ads related to "losing weight" might appear---you lose "pounds" when you are on a diet program. In fact, this is a real example. There are certain ways to "disable" portions of your webpage for matching with ads by Google.
Post More FrequentlyThis one is actually an SEO related tip: A new page when indexed by Google is given a boost in page ranking, i.e., fresh content is given an initial boost. However, after a certain time frame, your same page will go low in ranking unless people start linking to it. So, the more frequent you publish, this new-entry-benefit will be capitalized more often by you.
Getting ViralNothing will beat the joy of getting noticed on one of the social network sites. If you somehow hit the top page of Hackernews, Reedit, Digg, etc. your earnings can literary break all previous records. So, do think of submitting a well written article to these sites. You can also use Twitter and/ or Facebook to let your friends/ contacts know of something interesting you have written.
 Referring to Pakistan here as the "buying power" of the visitors to your website can result in significant revenue differences when an ad is clicked.