When writing a new post, it is never foreseeable how popular it will become. Sometimes a quick write-up may turn into a smash hit, generating lot's of hits, while other, more well written articles are doomed to a shadowy existence. This may be something to feel a bit blue about, but when it comes down to business, success is all that counts at the end of the day. In AdSense terms, success means having to identify which articles get the most attention by readers, measuring their payout and optionally tuning them for a better performance.
The first step, identifying popular content is a rather trivial thing to do. Install the Views module and activate it's "popular" view. It is advisable to also edit the view in order to limit access to authorized accounts. The navigation menu should contain an entry "Popular content" afterwards, which will list all pages, ordered by their popularity.
When a page emerges as being popular, that is, when it attracts visitors over an extended period of time, assign an URL channel in the AdSense setup to measure it's click through rate and eCPM. An URL channel showing an eCPM of close to or less than one dollar and/or a CTR of less than 1% signals, that the according page is in need of tuning.
Tuning a page is more of an art than science, not always possible and in some cases may even have an adverse effect. When experimenting, make sure to always create revisions of the pages in question. Also keep in mind, that changes may take up to 48 hours to take effect.