Ideal gears are Nex armours and chaotics, surge box and arc stream when making to RS gold the higher damage and Divine/Elysian/Chaotic/Drag defender for Supreme, depending on if you are comfortable flashing soul split while Prime is about you or not. A lot of cannonballs will be wasted on Spinolyps, so plenty of people prefer to not use a cannon, but it will speed it up a whole lot.
If you don't want to tank Supreme, don't attract a cannon (or if you do, time that your kills/placement perfectly so cannon only hits Prime or Rex (or Prime dies before Supreme spawns and vice versa)) and kill your tank 3 (or only Prime/Supreme if Rex does not disturb you) while praying mage/turmoil. Subsequently, kill Rex and Prime quickly when Rex expires, then execute and kill Supreme before repeating.
This method is a lot slower and, arguably, takes more preparation and you're far more vulnerable to crashers messing up your own instincts, but you ought to be taking no harm whatsoever except in Spinolyps, so for novices, it will be easier, particularly if you're not knowledgeable about the kings' maximum hits and if to flash spirit split/etc.
You shouldn't need a yak in case you have done the elite frem journal, however, it's almost essential if you haven't, otherwise, you lose out to a large part of your profit and it's not even worth DKing at the first place if you don't DK for pleasure, not profit (such as me).
In general, if you would like to be good at murdering any boss, research and try out different approaches yourself. I rarely see anyone else with a titan at DKs, even though it increasing your kills/hr massively, you can't charge the hides without sum pots either (as you kill the kings too fast), and having frem boots 4 signifies that buy osrs gold safe in case you bring friends it doesn't matter how quickly your skills are, you won't have to think about your yak scroll exercising. If you have any additional questions feel free to reply here or comment on my website asking, my PM inbox is 1386% full currently.