I've been an content publisher for some time now, and it would like to share some techniques that helped me and may help you to increase your monthly Adsense return and CTR.
1. Blend your Ad background into your content. Nothing turns off a site visitor more than a site that's full of lots of ads. Take a controlled approach to your advertising, and make your Adsense ads look relevant, helpful content instead of money drawers.
2. Stay away from the Default Template that Adsense provides. As website visitors, we have all become oblivious to the default Google Adsense layout. Alter your palette, and bring an original look to your site's Adsense units.
3. Use Blue Links. This is one of those human things, people love blue - it's a safe color and visitors like to click on blue links. Everyone's used to it. So stick with the blue links, and test lighter/darker versions of them.
4. Use fewer Adsense Units. When I switched from 3 adsense units to 2, I experienced a quick boost in CTR. Many of your Adsense units go unnoticed, which hurts CTR and CPM. Experiment with few Adsense units, and see if it helps your CTR or not.
5. Don't stand still, keep testing new things. This is the most important concept of all, don't get complacent with your CTR. You can always do better and drive up your returns, use channel tracking to follow your changes. Keep testing and tweaking your site.