Gold Ore terraria best places to farm?

Answer 1

If you go down to the third layer underground all the different ores become more common.

You can find out more in this guide: http://nerd-age.com/?p=175

Answer 2

Gold ore is usually located at 200 feet or below.  (only miniscule amounts above that height)

If you go into a large cavern going down (usually one from the surface)  You will see atleast 1 vein of gold ore.

Hope this helps abit.

Also use a terraria mapper to find ores if you need it.