Welcome to a Comprehensive Guide to Farming: An Overlordly way to gather Resources, I hope this guide may help new or intermediate players that decided to give a chance to this joy of old.
Let's start with the basic, what is Farming? Farming is a way to gather not only Lifeforce (The Main Fuel of your Dark Reign), but also Gold and Weaponry for your Dark Horde of Minions without having to clean up areas again and again and again... Only describing makes it look boring, you see?

Worry not, my Overlordy friend. With this guide you won't have to worry about any resource never again.
Tho I would recommend not to use it unless you're very desperate, using it to play it cheaper or easier makes your first time a little bit
dissapointing nonetheless.

As you play through the Infernal Abysses (Which is highly recommended) you may find MOULDS.
But what do moulds serve for? Moulds give you access to Unique Items to be forged in the Dark Tower, one of this moulds (Heaven's Peak Abyss') gives you access to the Harvesting Helmet, the ultimate item to FARM LIKE A GOD.
For this, I recommend that you play the Heaven's Peak Abyss BEFORE ending the game and get the mould for this helmet for the farming that is to come.
But what does the Harvesting Helmet do to be such good? Harvesting Helmet DOUBLES your Lifeforce Income, which is good when you want to infuse weaponry, armours and helmets. And obviously to increase your Dark Horde to incredible numbers.

This is the most simple yet obnoxious farming, but it has its rewarding.
Lifeforce is the fuel of your little minions that do everything for you, but is not only that. Lifeforce allows you to Infuse.
Infusing is, basically, pumping up the stats of your weapons, armors and helmets by using Minions, this grants a lot of bonuses that
may or may not be good, such as Fire Damage, Health Regen, etc.
How you infuse the items you'll forge I leave it up to you.

Why is the most simple yet obnoxius farming? Easy, remember those annoying, big beettles you see everywhere you go? Beat them everywhere you encounter them. The Tower Dungeon gives you the chance to fight them again everytime you want, thus giving you an infinite source of Lifeforce as they're relatively easy to kill.
Normal Beettles = Brown Lifeforce
Fire Beettles = Red Lifeforce
Toxic Beettles = Green Lifeforce
Magic Beettles = Blue Lifeforce

Defeating a group of Beettles in the Dungeon having equipped Harvesting Helmet gives you up to 150 lifeforce points everytime you beat them, so this is practically the most common and easiest farm to achieve.

I assume you're reading this because you chose the "Not being a ♥♥♥♥♥♥♥♥" Way of Playing and prefered the lesser evil, I'm none to judge you. This one is also pretty easy to achieve, when you make it to The Golden Hills you'll visit a Gold Mine in your way. This Gold Mine contains A LOT of barrels full of gold chunks, and when I say a lot, I mean it. Simply ransack the entire mine, teleport to the Tower and back to the mine, repeat all the times you want for infinite gold.

Or just be a ♥♥♥♥♥♥♥♥, like I do most of the times and choose Gold over your slaves everytime you can, not an infinite resource of gold but it's hard to run out of gold this way.

This may be hard to achieve, as there are few zones that have equipment for Minions close to Tower Portals and I admit I'm a bit lazy, but just find a zone full of crates you know there are weapons, order your minions to sack it, then rinse and repeat, much like the gold farming, this one is harder as not every crate in the game drops Minion Equipment.

So this would be mostly the guide to farm, some recommendations are to find ALL the Smelters (Trust me, It's way too much worth) and to use mostly Brown Minions for the Lifeforce Farming, also don't fear to expend minions in the Harvesting Helmet, it's worth the loss and you'll recover very quick with it. And that's all, folks. Tell me if you liked it and what could be improved for my next guide, sorry if I commited some mistakes, it was my first guide and just wanted to lend a friendly hand to the unnexperienced new players as this is my favourite game of all times. And remember: Is Good to be Bad ;)