The generic walkthrough is explained well on the wiki. Make sure to bring Ebon Vanguard Sniper Support as it eases up a lot of the encounters due to one-shotting foes.
Activate the G.O.L.E.M. 2.0s at each level, chosing the Ranged mode every time.
Level 1
Clear through to Renk and Sokka, then progress to the Ebon Vanguard (Captain Langmar, Chance Redding and Jenn Valefield) and then directly towards the gate of level 2.
Level 2
Dryads and Destroyers are hostile towards another, use that to your advantage on your way to the Norn. There are various way to handle the coming assault, running an SoS build trivializes the encounter to pulling single groups of Destroyers and focussing them down abusing the longbow range of spirits and the height of the hill at the bridge (spirits do attack and the Destroyers just stand there).
Follow Olaf Olafson to the gate and proceed to the Central Transfer Chamber in level 3
Level 3
Clear out all Destroyer groups before approaching the Disk of Chaos.
The boss can be kited, aggro can be diverted to the ranged G.O.L.E.M. 2.0s which you can always reactivate for 15 energy each.
Video links
Shiburito R/Rt
Serial E/Rt
Shade A/R
nightquist pure A
nightquist pure D