These should be labeled under common sense instead of secrets, but I've seen way too many sites that overlook many of the following:
1. If you have a business, don't sacrifice your products/services for the sake of placing your AdSense (or other) ads. You need to choose what your site is really about, showing ads or your products/services. You can show ads AND sell your products/services, but the ads need to be tastefully placed and flow with the content of your site. My recommendation, however, is to NOT place ads on any page where you are trying to sell something because it gives the user less choices to click away from your product.
2. Google allows you to block out competitors ads. USE THIS FEATURE. I've seen so many sites that just throw up AdSense on their site and it promptly displays ads that send traffic to competitors. Would you rather make a sale/conversion, or get $.10 for a click? It boggles my mind when I go on an SEO site and see Google ads for SEO services. If you're going to have ads on a site like that, you might want to go with a different ad provider (at least on that page) so you can display a complimentary rather than competitive ad.
3. Worried about where to place your ads? Google has recommended placement:
https://www.google.com/adsense/suppo...y?answer=17954.
4. Trying to optimize your ads? Try testing. Google provides channels so you can track which ad units perform best. Make use of them. You can also use AdSense in conjunction with Analytics, which provides a click-through rate for every link on every page on which it is installed. Wondering about what to test? Try unit size, colors, text vs. image vs. banner, placement...and anything else you can think of.
5. Is nobody clicking on your ads? Well, what does your content look like? If you have content that is poorly written, poorly edited, not useful and it looks like it's been just thrown up there to bring people in to click on the ads, no one is going to click on them. Write for your users, not for AdSense. If you offer no value to anyone, you're not going to get any appreciable traffic or clicks.
There is a lot more that I could write, but I'll probably do it in a blog post sometime in the future. I hope this helps a few of you.