Shield, burst and blast
 Psyker Build - Warhammer 40k: Darktide 

It's all about repeatedly popping a shield, quick brain bursts and staff blasts.

At full warp charges, combat ability will regen fairly quickly, so don't be shy about using it, followed by 5-8 brain bursts thanks to the kinetic resonance, which can clear a rush of elites, or those distant ranged threats. It's also a great opener against bosses, that many brain bursts shaves off a huge chunk of their health.

Staff is your primary weapon: bolts  against singular/couple enemies, while also being great at triggering suppression, blast to deal with crowds and hordes, great tool to stagger anything, even brutes at full charge. I like the suppression perk as blasts are often used defensively at close range (keep aiming it at your feet to clear throw enemies), and crit to help both fire modes.

Blaze sword is for its great defensive ability, you'll be able to easily tank a daemonhost with it, so long as you have extra stamina and deflector: if your toughness is down, or you need to cross an area with shooting hostiles, swap to sword and start deflecting. Illis specifically to help against swarming hordes, just remember to block/block-push, charge sword then slice. And always dodge.

Path is a mixture of offensive and defensive, focusing on support.

Curios are also a mixture of stats: at least one wound since psyker are so low on that, defence versus bombers and flamers since you'll invariably be in a choke point/skull-rest thingie controlled by them, and a little extra corruption resistance, since I hate it (at pre lv 30, worth having +experience on all curios, then swap when at max).

Ultimately, just shield, burst, and blast.