AdSense Elite

1 - Register with Google AdSense website: www.AdSense.com or www.google.com/AdSense
2 - Wait for your Google AdSense account to be verified, and then copy your Google AdSense code.
3 - Download and install this Google AdSense extension for Joomla!
4 - Paste your Google AdSense code in the extension parameters and publish it.
5 - If your Google AdSense account is not yet activated, you will see a blank space instead of Google AdSense ad unit. You have to wait 1 or 2 days for your Google AdSense to be activated and serve Ads on your site.
After having an activated account, you can copy your module to 2 other module positions (you can have 3 ad units in the same web page - Google AdSense Ad implementation policies.) and change all the optional settings if you want so.

From your AdSense Elite extension parameters:

You can chose ad unit alignment or enter a custom CSS code.
You can block some Ip address from viewing your Google AdSense ads.
You can limit Google AdSense ads to be seen just by guest/registered/all users.
You can block Google AdSense ads on article view.
You can change Google AdSense ad format.