This question always gets asked a ton around here.
IMO the easiest way is to grab GatherMate, GatherMate_Data, and Routes. Routes draws a line on the map with the easiest route to take when farming professions.
http://www.wowace.com/projects/gathermate/
http://www.wowinterface.com/download...01-Routes.html
http://www.wowace.com/projects/gathermate_data/