Since there is a lot of Grind invloved and it can become time consuming and boring,
here are some suggestions to reduce frustration and increase efficiency.

I will describe what is needed but it is up to the individual to reach the requirements.

If something is missing, wrong, outdated or unclear, feel free to ask and discuss.
Missing information will be added, if requested.

• Major Soulstones
  
• specific Materials

https://steamproxy.com/sharedfiles/filedetails/?id=3524085676

• nothing - due it's random Nature

https://steamproxy.com/sharedfiles/filedetails/?id=3524085706

• Minor Soulstones
  
• Prestige
  
• Void Essences
  
• random Materials

https://steamproxy.com/sharedfiles/filedetails/?id=3523965012

There are some Unlockables, that can either increase Prestige or Materials at significant Rates.
Those should be used before attempting heavy Farming.

Arduous Training - Increase Prestige gained by 40%.
The Samurai - Prestige Level: 41 (21 Prestige Points)
https://steamproxy.com/sharedfiles/filedetails/?id=3524070335
https://steamproxy.com/sharedfiles/filedetails/?id=3524062450
Efficient Extraction - Increases the Amount of Materials collected by 50%.
The Arcane Weaver - Prestige Level: 41 (21 Prestige Points)
https://steamproxy.com/sharedfiles/filedetails/?id=3524070399
https://steamproxy.com/sharedfiles/filedetails/?id=3524062411
Material Harvest - Bonus Materials when picking up Major Soulstones.
The Legionnaire - Prestige Level: 61 (41 Prestige Points)
https://steamproxy.com/sharedfiles/filedetails/?id=3524070371
https://steamproxy.com/sharedfiles/filedetails/?id=3524062387
The Engineer - Prestige Level 47 (27 Prestige Points)
https://steamproxy.com/sharedfiles/filedetails/?id=3524070455
The Cursed Captain - Prestige Level 47 (27 Prestige Points)
https://steamproxy.com/sharedfiles/filedetails/?id=3524070430
The Machinist - Prestige Level 47 (27 Prestige Points)
https://steamproxy.com/sharedfiles/filedetails/?id=3524070487

Prestige Levels are required for unlocking Skill Points in the Character Skill Trees
and for unlocking various Runes and Skills.
Minor Soulstones are a Common Currency to unlock Characters, Weapons and Skill Tree Perks.

Best Starting Map for Farming Endless + Overlord: Scorching Vally (Danger Level 0)
The Bonuses for Minor Soulstones and Prestige will max out at Curse Intensity 36.
To achieve the max Bonuses, minium Curse Intensity for each Curse Tier has to be reached.
Curse Intensity is freely customizeable,
as long as the minimum Curse Intensity per Curse Tier is met.
IMPORTANT
Curse Intensity above minimum requirements will NOT yield any additional Bonuses.

• +365% Minor Soulstones
  
• +600% Prestige

https://steamproxy.com/sharedfiles/filedetails/?id=3524002314
The Bonuses for Prestige and Minor Soulstones have no Limits and will increase further with higher Titan Hunt Difficulty.
IMPORTANT
All other Materials are avaible at Titan Hunt - Sigil V +0 but Drop Rates will NOT increase further after this point.

• +400% Minor Soulstones
  
• +350% Prestige

https://steamproxy.com/sharedfiles/filedetails/?id=3523965012
In direct comparison, considering Endless + Overlord went into Loop 4 and
Titan Hunt V+0 ended after defeating the Void King.

~ 16.5k Minor Soulstones per Minute
~ 43.3k Prestige per Minute
https://steamproxy.com/sharedfiles/filedetails/?id=3221459741
~ 14.6k Minor Soulstones per Minute
~ 88.9k Prestige per Minute
https://steamproxy.com/sharedfiles/filedetails/?id=3221459930
~ 26.0k Minor Soulstones per Minute
~ 157.8k Prestige per Minute
https://steamproxy.com/sharedfiles/filedetails/?id=3523965056
While there is a minor loss for Minor Soulstones in Overlord compared to Endless,
the amount of Prestige is far more superior.
Titan Hunt beats both and has Potential for higher Prestige and Minor Soulstone Rates.
The decision is up to the indivudal, my personal choice would be Titan Hunt.

Major Soulstones are needed for the Skill Trees, for crafting Weapons and for unlocking Characters.

Best Starting Map for Farming: Scorching Vally (Danger Level 0)

• Lord Spawns can be increased with House of Lords (Curse III, IV, V)
  and are maxed out at 4 per Wave.
  
• Lord Kill Speed can be increased with Council of Lords (Curse III, IV, V),
  which will allow all 4 Lords to spawn simultaneously.

Total Curse Intensity - 12
House of Lords x3 (6) +3 Lords
Council of Lords x3 (6) 4 Lords spawn at the same time

Since Major Soulstones are dropping from Lord's of the Void, Overlord is the way to go.
Easy way if done on lowest possible Curse Intensity.
Major Soulstones should only be farmed, if desperatly needed.
https://steamproxy.com/sharedfiles/filedetails/?id=3221531878
IMPORTANT
At low Curse Intensity and with a moderate Build, Overlord 6 is easy farmable.
But at Overlord 7 the Enemy HP Scaling will jump from 52k to over 500k,
which then will take significant longer and may become unefficient.

The various Materials are needed for crafting Weapons.

For every Material Tier a certain Curse Tier is requiered.
If you want to farm a specific Material, you only need the respective Curse Tier.
E.g. if you want Legendary Materials, you only need Curse V (6/6).

• Curse 0 - Common (White), Uncommon (Green)
  
• Curse I (4/4) - +20% Common (White)
  
• Curse II (4/4) - +20% Common (White), +20% Uncommon (Green)
  
• Curse III (5/5) - Rare (Blue), +20% Uncommon (Green)
  
• Curse IV (5/5) - Epic (Purple)
  
• Curse V (6/6) - Legendary (Yellow)
  
• Curse VI (6/6) - +20% Common (White), Void Essences

Void Fields are better suited for farming specific Materials, since those are fixed per Map.

Material Drops and Rates depend on the Sigil and are fixed.

• Tier I - Sigil of Curruption
  +20% Common (White), +20% Uncommon (Green)
  
• Tier II - Sigil of Vileness
  +40% Common (White), +40% Uncommon (Green), Rare (Blue)
  
• Tier III - Sigil of Wickedness
  +60% Common (White), +60% Uncommon (Green), Rare (Blue), Epic (Purple)
  
• Tier IV - Sigil of Hate
  +80% Common (White), +80% Uncommon (Green), Rare (Blue), Epic (Purple), Legendary (Yellow)
  
• Tier V - Sigil of the Void
  +80% Common (White), +80% Uncommon (Green), Rare (Blue), Epic (Purple), Legendary (Yellow), Void Essences

Titan Hunt is amazing for Farming, if no specific Materials are needed.
On Titan Selection, there is a Preview of Materials avaible below the Titan Portrait.

When the Lords die, it is important to IGNORE the dropped Major Soulstones.
The amount of Materials harvested from them scales with Kill Progression.

Starting in any corner of a map, simply killing enemies as fast as possible, until the Lords spawn.
Since pathways of enemies are shorter, when they spawn in corners, the whole kill process runs alot faster.

After they are dead, moving to another corner is adviced, to not accidently picking up a Major Soulstone, while dodging or running around like a headless chicken.

Repeating this process for the next three Lord Waves.

The final Wave can be killed anywhere. All Major Soulstones will be collected automatically after the round ends and turned into tons of Materials.

Same Strategy, but due the random Nature of Shrines there is no specific Movement Patter.

Not picking ANY Major Soulstone until the end VS picking Major Soulstones instantly.
https://steamproxy.com/sharedfiles/filedetails/?id=3220177303
https://steamproxy.com/sharedfiles/filedetails/?id=3220177690
The Numbers speak for themselves.
The amount per Material Node scales with kill progression.
This rule also applies to the material gain via Material Marvest and can be further increased with Efficient Extraction.
So all Bonus Materials gained from Major Soulstones after the round ends, will be scaled based on the final kill progression.

Void Essences are special Materials, that are linked to the 7 Lords of the Void.

• Eye of Pestilence - Alexi, the Plague Bearer
  
• Eternal Core - Tiaggro, the Eternal Guardian
  
• Fragment of Fire - Gammuth, the Incarantion of Fire
  
• Fragment of Ice - Colummeth, the Incarnation of Ice
  
• Helmet of Corruption - Aelfraed, the Fallen King
  
• Horn of Chaos - Allaxiz, the Chaos Bringer
  
• Scales of Profecy - Keythaiz, the Prophetess

The best place to farm them is in Titan Hunt - Sigil of the Void (Tier V) +0 and above.
https://steamproxy.com/sharedfiles/filedetails/?id=3523965012
w/ Material Harvest + Efficient Extraction

• 48x Eye of Pestilence
  
• 38x Eternal Core
  
• 38x Fragment of Fire
  
• 33x Fragment of Ice
  
• 27x Helmet of Corruption
  
• 30x Horn of Chaos
  
• 38x Scales of Profecy

TOTAL = 252
https://steamproxy.com/sharedfiles/filedetails/?id=3523965056
w/o Material Harvest + Efficient Extraction

• 28x Eye of Pestilence
  
• 26x Eternal Core
  
• 23x Fragment of Fire
  
• 28x Fragment of Ice
  
• 25x Helmet of Corruption
  
• 12x Horn of Chaos
  
• 24x Scales of Profecy

TOTAL = 166
https://steamproxy.com/sharedfiles/filedetails/?id=3523965087
Efficient Extraction will give a significant boost to Void Essence Drops.
Material Harvest can be usefull, but chances to gain Major Soulstones from Lords is random.

Feel free to discuss and comment.

If you have any suggestions, feedback or questions, don't hestitate to post here.

Cheers!