The most efficient way of tracking traffic from referring sites via Google Analytics is by tagging the traffic with specific variables that are recognized by Google Analytics.
All you have to do is attach those three variables to the URL: utm_source, utm_medium and utm_campaign.
For example: http://www.royaldeerdesign.com/?utm_source=google&utm_medium=cost-per-click& utm_campaign=June2011
Google provides even a tool URL Builder that can be found here.
