instead of just bashing Adsense with most of my post here on this forum I'm going to give away an Adsense tip i learned.
If you have an adsense custom search box place a link unit under of it.
check out how Ezine articles does it: [
ezinearticles.com...]
I refer to it as suggested search term.
example:
someone goes to your search bar to search to find more info, and what's there? Generic Key terms related to your sites theme "ie Adsense link units"
I would not recommend putting them above the fold. The click rate is super high, but remember link units clicks pays less.
when i first put them above the fold "in the same location as Ezine Articles" my ctr tripled, but the average CPC was 70% less, and my other ad units CTR dropped.
Also if you have a blog type of site, and have a related articles section, put a link unit in at the bottom.
Also, InfoLinks "Tag" works great here also.
Disclaimer:
All niches are different, so test it for yourself.