He generally excels in close quarter combat with his flamethrower, do not get close up to him and do not waste ammo, like Lieutenant Lech Kril, he is invincible with his generator still covered. The generator will usually become exposed for a short while after his attacks, often after using his abilities. Keep your eye on him and shoot at the generator when it is exposed.
Having teammates surround Ruk at all times will allow a flexible attack to wherever his weak spot is.
It is hard to dodge his Fire Blast (Ruk), tanking the damage with your shield is a viable alternative, as the said fire only deals 300s damage. You can also attempt to hide behind cover, just make sure it's big enough to shield your entire body (or you can crouch in cover).
When he uses his most dangerous ability -- Inferno is when he is the most vulnerable. The generator on his back will always be open after using the ability, flank your way to his back and blast away while being careful of stray pillars.
Utilizing Warframe AbilitiesEdit
Ash's Teleport will teleport you inside his wall of fire for an easy retaliation.