If you want to maximize your revenue you have to test your placement. Identify poor performing ad placements and try to understand why they aren't doing well.
Is the skyscraper banner on the right side of your site performing poorly because it is on the right side instead of the left? Is it because you have a fluid layout instead of a static layout? Is it because the color scheme sucks? Is the color scheme right, but there is a border around the ad?
There are a million questions and theories you could think of to explain why Adsense is doing what it is doing. Ultimately you have to test the theory to find what the reality really is.
In order to test Adsense you have to set up channels for individual ads.
If you aren't already using channels then you will need to log in to Adsense and retrieve new code. Before you set up a new ad unit click on Channels under the "Adsense for content" tab.
You can add a URL Channel if you run many different sites and want to break down the performance of a single site. In order to test different units on a single site though you will need to set up some Custom Channels. There are several different ways to choose to do this.
The first way, and it only works if you have a small site, is to set up a custom channel for every page. It is very tedious so I don't recommend it.
Instead, create a channel for each different ad unit you plan on using. For example, make an "adlinks" channel (tip, name the channel in this format: "Your Site Name - adlinks".), a right skyscraper channel, a top leaderboard channel, whatever you need. Once this is done then you can go back and set up your new ad units.
Now you will be able to identify which Adsense ads are performing the best and which are performing the worst.
Be aware, stats for channels is even less steady than your overall Adsense stats. The best way to measure channel performance is to average together three or four days of stats, or if your traffic is low, possibly for longer to allow for any statistic anomalies.
If you haven't done so already, Read Google's Terms of Service. If you are unsure about using a particular technique then send them an e-mail and ask!
I'm not going to repeat the rules here. Google is changing their terms of service regularly. You need to be paying attention when they update them.
There will always be publishers who choose to blatantly break Google's Terms of Service for Adsense. Unfortunately this only decreases the quality of Adsense traffic to advertisers. Ultimately advertisers choose to lower the amount of money they are spending on the Adsense publishing network.
Do yourself and every other webmaster a favor. When you see a website openly breaking Google's Terms of Service report them.