Crit Balls
 Psyker Build - Warhammer 40k: Darktide 

This build is based around the Surge blessing.  Electrokinetic staff has a built-in 15% crit chance bonus with maximum Critical Bonus stat.  Just using the staff you will be at 48.5% crit chance.  This will quickly climb over 75% using Scrier's Gaze.  3/4 primary attacks will be double-shot crits.  Aiming for heads is not super important, feel free to just target center-mass.

Left-click-spam warp balls destroy all targets except Crushers and Bulwarks; use your lightning secondary on them.  For Armored Ragers target the head or use lightning secondary.  If you're nervous about a dangerous special juking your balls (pox hound, trapper) hit 'em with the lighting!

Melee Weapon is up to you.  I picked this one because the worst thing for Psyker is to get surrounded, and the MkVIII Force Greatsword should help in that situation with its force push and wide cleaving sweeps.  Your sword has enough stamina and block cost reduction to secure a rez with enemies around or block and dodge out of a bad situation.  It is mainly a defensive tool.

Use Scrier's Gaze liberally, cooldown is super short.  You can keep it up permanently if there are enough elites/specialists to kill, so you never need to quell.  If there are no elites/specialists around you can quell to stay in Scrier's Gaze longer for the juicy bonuses.

Massive crit chance + Empathic Evasion makes you basically immune to ranged fire as long as you're hitting enemies with primary spam.

If another Psyker is using Prescience you can switch to one of the other auras.

If you want to focus on lightning rather than balls swap Surge for Warp Flurry.

If you're on PC get the "Warp Unbound Timer" mod so you can go ham during the 10s grace period without blowing up.  It's tough to see when that timer ends without the mod.  I also recommend the "FullAuto" mod because this is an RSI build.

Have fun!