You start the combat with it , as you aproach from afar(so you got some space), you use it to weaken enemy armor .... you can also combine it with yrden if enemys are too fast .It does not stagger an enemy at all, so if i use it on drowners, they just come up and punch me in the face.. It seems prretty useless unless Im fighting someting incredibly slow.
What is the proper way to use it
well it is a short range ability. (at least mine is- just short range sparks)You don't use fire stream up close. Fire stream is super OP if you use it correctly.
Think of it like a blowtorch weapon.