I've found the best way to improve CTR is to make sure you use section targetting code if in a blog wrap the code around your title tag.
This will serve up more relevant ads and CTR and earnings will improve measurably.
Learn about section targetting here
Then check your ad layout/placement ,If you use these methods you should see an increase in CTR.
http://adsense.google.com/support/bi...y?answer=17954
http://adsense.google.com/support/bi...?answer=132575
Forget Adsense books they are repackaged/outdated/recycled crap designed to make the author money only.
Most of the advise in e books will get you banned from adsense.