Witch
Lich
Essence Drain and 
Contagion have been the absolute bread and butter for the 0.3 league start!
With the new addition of the abyss mechanic these two skills will blow up anything that stands in your path.
This guide will walk you through an early campaign scenario and how to get into maps to start farming!
As early as level 2 you will have access to Contagion this ability is essential like a real world virus. If you cast it on a mob and that mob dies it will die and spread to other mobs and increase in damage! Along side Contagion you can grab 
Frost Bomb to help you clear mobs and bosses early until you get some more skills!
Once you reach level 6 you will have access to Contagion. This will be your big damage dealing skill that will help you kill mobs very fast! The rotation becomes Essence Drain into Contagion and the pack of mobs should die!
As you progress through Act 1 to try group up mobs so you can cast this 2 button combo and blow up any packs! ALSO DO ALL THE ABYSSES THEY DROP A TON OF LOOT AND ARE GOLD MINES FOR CURRENCY!
For your first 30 spirit I grabbed 
Arctic Armour you can grab 
Withering Presence instead for more damage. Arctic Armour for survability Withering Presence for damage.
Once you get into Act 2 you will have access to 
Bonestorm this skill will help you kill rares and bosses a lot easier. Its a bit of a harder skill to get used to but once you have it down pact things will just fall right over.
In Act 3 you will eventually get access to 
Dark Effigy this will be a big damage dealing skill and help you just blast your way through harder mobs alongside Bonestorm. Something to keep in mind Dark Effigy will only attack mobs that have a CHAOS DOT on them so you need to make sure you cast Contagion or Essence Drain first to get the damage rolling.
A really good combination with Dark Effigy is to pair it with 
Flame Wall so you can get extra damage.
At this point for mobs your rotation is Essence Drain -> Contagion
For rares you want to do Essence Drain -> Dark Effigy -> Flame Wall
Once you get you next set of spirit and hit 60 spirit you can temporarily drop Arctic Armour and replace it with 
Blasphemy and 
Enfeeble or you can do 
Temporal Chains. This will help keep your mobs crowd controlled.
This setup will hold your hand essentially through the rest of the campaign. Just make sure you keep up to date with your gear!
+SKILL GEMS and +SPELL DAMAGE is huge for damage. Prioritize Spell Skill Gems or Chaos Skill gems then Spell Damage. Every point of Skill gems you get will be actually massive for damage so dont sleep on it!
Note put a higher priority on +Skill Gems
Once you get out to the end of the campaign and early maps you will eventually make your way to 
Whispers of Doom notable. This will allow you to have 2 curses. Once you have this setup you can follow the skill gems down below.
Essentially what this allows us to do is both have Enfeeble and Temporal Chains to essentially make the mobs never move and deal extremely little damage. On top of that when we pair it with Cursed Ground any mobs that come onto it will just be stuck to a standstill.
What this allows up to do is use is have all the enemies slowed, dotted, cursed and essentially spreading a virus. Once you get to this stage of the build then I would recommend picking up the 
Windscream boots
