Ok, let's hear them. For everyone here that uses adsense, share your tips on how to increase your Adsense CTR. What worked? What didn't? Here are some of mine.
Above the fold increase CTR
It is pretty simple but if a visitor can't see your ads, they will not click them. Put your adsense above the fold. The first thing on the page, after the header if possible (or even in the header).
I like to put two blocks of ads right above the main content and one in the sidebar or midway. This seems to work well for most of my sites.
You can have up to three ads and 1 link
Again, simple enough. If you have only 2 ads, that is only 2 chances the visitors have to see ads. Google allows you to put three ad blocks and 1 link tree thing (I forget the name). Use all three and place them in various spots.
Track the Ads
Each time you generate an ad from Google, you can add parameters that track that ad alone. Do this and play around with it. Determine what works best, which format or change gets the most clicks.
Format types matter
Ad format types/sizes changes Adsense CTR. There is no golden rule although Google will recommend certain ad formats over others. Play around and see what works. Record your results so you can keep track of them.
For the most part, you want your ads to blend in with your content as though they are a part of your main content. Right in the center of a text block is great if you have all of your colors matching. You can't remove the "Ads by Google".
On the flip side, I've heard of great success from people using complete opposite colors which stand out. I've never had this deliver a higher CTR than using matching colors. Try it and see what works for you.
Text vs. Image
Text has always yielded a higher Adsense CTR than an image but an image looks nicer. Try both and see what results you have or allow adsense to deliver both types.
Most people don't mention traffic when they talk about Adsense CTR increase but I think it is important. Where your traffic comes from matters for ads. I've found that organic traffic from search engines converts much better than most other types of traffic.
Members rarely ever click in my experience, it is 80% of the time guests who click ads. Because of this, I typically disable most ads for members as this makes their experience better. They will start promoting your site socially and via other methods which bring more guests but if you bombard them with ads and make them hate your site, they will not.
That is all I can think of off the top of my head. What are your tips?