Well generally , defiant set, a decent amount of hp varying from 100k to 300k, some dmg and Dmg reduction . My build is very different as it deals insane dmg and low HP which is 37k HP. Cerebral Vortex as a defense so when people hit you, the torrents proc on them and you deal dmg and probably stun them.
Stun element because it stuns and it gives stack debuff. Up to 50% more dmg as well as the stunning. Also ice can be useful because it reduces move speed and Dmg of other players as well as potential frozen.
Stun resist to reduce amount of times you get stunned.
Lots of dmg reduction and balanced with high HP and decent dmg. Defiant is a good set because it gives you more dmg and Dmg reduction as your HP gets higher. Shieldwall as proc, skullshields, battle mage, toss, possibly enigma, earthquake or cosmic orb, earthshatter, a chest mythic and sanctuary to survive death and strike back.
High HP gets obtained by vampiric touch, a lot of epic HP affix, battle mage ,fauns gift with luck, plagued and even crystal hp%. Dmg reduction by shieldwall, possibly MP absorb depending on the build, defiant, skullshields for wizard, Equivalence and other ways.
I'm not really good with making those general high HP builds so it's hard to help you there. All I can say is discover what works best and see how far you go. See what needs improving and keep pushing yourself.
You may need many crystals saved up to learn. You can also post your build if in doubt for improvement just in case. Good luck on your journey .