Building and Farming for Currency items
Path of Exile deviated from the conventional monetary system of MMORPGs. You won't find gold coins, bars, dollars or any name of currency in the game, what POE introduced is called Currency items. They are obtained by looting enemies, bought directly from shops or NPC's, or obtained via the Vendor Recipe system by trading specific Path of Exile items in exchange for a set number of Currency items. It may sound confusing at first but once you get the hang of it, Currency items is a creative and unique aspect of POE that you won't find in any other MMORPG.
Farming for Currency means several grinding runs on a spot that yields valuable Currency items, most likely from blue or yellow mobs to speed up and raise the chances. Locate a spot where yellow or blue mobs spawn often and slaughter them repeatedly to obtain currency items and good gear that fetches a good set and amount of Currency items. The Docks at ACT III is a good choice for this strategy since yellow and blue mobs often spawn and are usually clustered in an area. Wearing equipment with Increased Item Quantity and Item Rarity would be extremely valuable in this case.
Farming speed is all about how quickly you can kill mobs. The main logic and thinking here is: the quicker and the more you kill, the higher your chances of acquiring good loot or Currency items. If your Exile is having difficulty finishing a mob before moving on to the next, then it would be wise to check your equipment, Links and switch Skills to try and see if your tweaked Exile can handle that area's mobs better. If you are still having trouble after checking all these factors then look for a different spot. No sense in trying over and over again to farm in an area where you die or run often.
Drop penalty is something to be considered as well. Farming a level 30 area when you are at level 40 or higher is not efficient and beneficial for your efforts to build your Currency items unless you can clear mobs in 1 to 2 attacks in which case your killing speed counteracts the penalty. Areas that are on level 60 and above is an exception to this though. Hope these pointers help you out with your farming runs!