1. Placement
There is no use in putting your adsense ads in a place where nobody is looking. So, if you turn this around, the best way to put your adsense ads is where everybody is looking!
This means, the top left corner, since we read English from left to right, top to bottom. Put it beneath all graphical banners you are using, and maybe also beneath a small portion of the text (this will prevent your readers to skip the ad, due to their subconsciousness adding it to the header of the site).

2. Colors
[ad] Two things come into play when it comes to colors.
First of all, make sure your ads blend in to your site. Don’t use flashy pink and green ads, when your website’s colors are grey and brown. Make the ads blend in, preferrably you change the backgroundcolor and the bordercolor to the color of your website’s background.
The second thing when it comes to colors, are blue links. Ok, I hear you yelling now! Blue links are from the days of yore, they don’t fit in to the design of my website, etcetera, etcetera. You are right. Very right. But, since blue links are from the days of yore, our minds are set to automatically recognise them, and thus, make them more clickable. And hey, now that’s exactly what we want, no?

3. Text and topics
Google Adsense ads perform so well because they are targeted to your audience. This means, that Adsense has to know what your audience likes. It does so by checking what your website is about, assuming that, since the person is visiting your website, he/she must find it interesting, and thus adjusting the ads according to your website’s topic.
One problem: it must be able to find out what your website is all about. It does so by scanning your titles, your metadata (keywords etcetera), your urls, and your content. However, if your website is called Rusty’s Ramblings, url rustysramblings.com, and you blog about just about everything you see, cars, the weather, your garden, politics, your significant other etcetera, Google’s Adsense spider will have quite a hard time to find out what your website exactly is all about. And thus, the ads it will server may not be all that well targeted, making you lose valuable clicks.
So, the moral of this ramble: keep your content close in the niche in which your website operates. Do you want to write about 4 or 5 different topics? Create 2 or 3 or even 5 different websites.

4. Switch from image-ads to text-ads, or the other way around
Check what works best for your website, and make sure it depends on the position of the ad!
I noticed, that for my websites, the text-ads work best, by far. Especially the in-content ads do not work at all when set to images only. Sidebanner ads can work as images, but it also depends on your website topic and layout. For instance, a website about divorces will perform better with text-ads, since people visiting your site are in a reading mood. On a gaming website, the image ads can perform better, since gamers are more in a graphical mood.

5. Test, trial and error.
The last but not least way to increase your Adsense earnings, is testing. Don’t be afraid, try out new things. You will notice that your earnings will decrease by some tests, but still, you have learned something there! Don’t be afraid! If you’ve never had the courage to test out standing on your two legs, and putting one foot in front of the other, and if yo udidn’t learn from falling and getting up again, you’d still be sitting on the ground now. The same goes for Adsense, try, and learn from your trials.
Make sure you give your tests enough time to perform. You may already have noticed that every day is a different day on your websites. Depending on your topic, fridays typically perform less. Or, in the example of the divorce website, weekends and holidays perform bad, since people do not tend to look up info about getting divorced, when they’re at home with the family.
Give your test a week time, unless you see a dramatic decrease (from 100 clicks a day to 0 or something).

Good luck with these tips, and let me know in the comments if these worked for you, or if you have other tips!

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