Anything you want. That's the short answer. Also avoid % values of WD and ED and only add flat damage values. Ideally have a fair amount of HP and sometimes reduction of damage or dodging attacks very well .
You will ideally want a balance build where you deal 50% damage and 50% damage reduction with around 80k HP or so, depending on the build but the Balance build won't use Battlemage since Battlemage is more for the high damage reduction.
For damage reduction, use Plagued, Fauns Gift, Cerebral Vortex (optional), Shieldwall in proc most of the time , skullshield , 1700+ Armour crystal affix , 170+ all resist crystal affix, talents such as cosmic, blessed, hardened , permafrost for MP Absorb , Ice to reduce DMG by 25% , Defiant . Heck even deadly arts if you dare yourself .
Also Satyrs spirit which uses gold find to increase MP and AR% as an option. Equivalence too . Summoners to reduce DMG by 3% per summon .
Obviously add 6× 1040 ED for damage or 7× if you have pet. Also 6-7× 1540 HP too. If you use Fauns gift, use Luck crystal affix and nature full of luck. Not only that but you can add 19% HP by crystal affix or 18% of both HP/MP on legend affix called Balance.
Add Sanctuary for any build to survive one death and even if the duration is one second, it's very worth it. Some builds don't need sanctuary due to them not dying as often. You survive a death but have 10% remaining HP.
For more tankier builds and builds that don't mind using Battlemage , Battlemage is good because 60% increased AR and HP . Scoundrel gives 60% HP and MP by Balance.
The other damage reduction can be achieved by 9% Hyper armour to reduce DMG whilst attacking and possibly double mitigate, though it's only 4% which is extremely low so it's not all that worth it but it can double reduction.
For damage, you can use Defiant, 6-7× ED, 18% Push the Limit or more , hit frequency skills and burst damage. Scalp can combine from 3 attacks into one massive attack to cause great bleed damage and OH% damage. Skullshield is an alive entity that will keep shooting , skullshield both reduces DMG by 10% per skull and deals 300% OH per hit and hits very fast. Another option is cosmic orb /orb due to hit frequency and Storm due to wide AOE and hit frequency.
Crits and Deadly strikes are an option too but they are not as worth it due to Eternal Flawless Victory trophies that nerf crit chance so much as well as reducing chance to elemental crit. You can use Coat skill or proc to fix that but you'll end up standing,being vulnerable to Cerebral Vortex (CV) but you can make clever A.I setups with a high crit character, mainly rogue in 2v2 . It's an option but the risk is less slots to be able to reduce DMG but it is an option nonetheless. After all, one shot builds were once a thing and super powerful builds in general.
Cerebral Vortex is mainly damage to deal once you get hit (% chance to proc torrent onto players)as well as possible Terrashaper to deal closeup damage of many craters as possible when you get hit.
Living Force to give 60% increased DMG to projectiles , Demonic to increase 60% DMG to players below 25% HP , Electrocution which is similar but deals 120% DMG increased after 4 stack debuff of shock at player below 25% HP and Execute DMG which works like demonic but as a legend affix.
18% Barbarian or 18% Glasscannon to increase DMG by 18% but they sacrifice MP or HP by 18% bht if you don't care too much, that's a good option for dealing damage.
Bleed dot , Amplify Talent , brutality talent , Empower if you don't care too much about HP and more for DMG.
Mythic wise: Discordance for special skills like orb or so to deal high DMG with cooldown of primary skill , Energy/Fury to deal DMG based on current missing MP% but Fury increase special skill DMG by 50% , Ruptured for bleeding players , Exposed mythic for dealing 50% increased DMG by pierce skills , cosmic orb for hit frequency and DMG , earthquake for stun and closeup damage ,etc.
Vampiric Touch increases HP by 75% and bleed DMG by 75%. It's always used . Perseverance to reduce dot DMG by 40% or more.