Guide similar to this have been made, but I will enhance them, as well as crush their efficiency. Also, I will NOT give you a bullshit estimate about how much gold I make from this, I will tell you the truth, I farmed up enough money within one week of farming when practically no one was playing on a server I had no connections on with a LEVEL 16 for my level 29 twink.
Code:
First, you need a character that can take a lot of low level kobolds and such, preferably level 13+ based on your class.
Second, you NEED this addon to MAXIMIZE efficiency, trust me, it works
Gatherer addon for World of Warcraft
Download the addon, as well as the DB for it from Wowhead (right below the addon downloads)
Follow this guide to properly work the DB for the addon
GathererDB - Norganna's AddOns
(On the bottom where it says "Usage")
After you get everything working on this addon, you will be able to configure the addon, such as make the icons for veins and nodes bigger, smaller, transparent, completely visible, etc. (This can be also used from farming higher level goods, so this guide can also help high levels)
Well, this is MY PERSONAL route:
The black line is the path I follow, I'm not sure if it's the most efficient, but it sure worked for me!
Coded for fun