My Loadout Management - will change depending on fun, feel, and availability of mods.

Primary: [Astilla Prime]
Secondary: [Twin Grakatas]
Melee: [Reaper Prime], or [Kuva Shildeg]
Helminth: Lull (replace 1)
School: Zenurik
Companion: [Sahasa Kubrow] (for Mecha set build); otherwise use your companion of choice

This build is for my [Ghost] Loadout. I've replaced Decoy with Lull. It may seem odd to have both Lull and Invisibility, but I find it very useful to jump into the centre of a tile and cast Lull to maximize the amount of enemies affected, and start doing finishers. This build is mainly used when I feel like playing stealthily; unveiling specific Rivens; leveling weapons; spy or capture missions; or for a change of pace.

I'm using a Scythe or Hammer stealth finisher build, as these weapons have the highest stealth finisher multiplier when enemies are unalerted, which they should be with Lull and Invisibility active.

Replacement Mods
You could replace [Loki]'s [Hushed Invisibility] augment with [Constitution]; or [Mecha Pulse] if running a Mecha pet build.
You could replace [Speed Drift] with [Primed Sure Footed], depending on the weapons you are using.
You could replace Enemy Radar with Mecha Empowered if running a Mecha pet build

Mecha Build - Use weapons with high slash, with either guaranteed status or slash, like [Glaive Prime], [Quassus], [Hystrix].

Playstyle
Keep your Invisibility (2) up during the mission. Keep your eye on the timer.
Cast Lull (1) when in a group of enemies, or when capturing a target.
Cast Radial Disarm if enemy numbers become overwhelming and to draw them towards you for a Lull cast.