The idea is to idle everything but the Cataclysm attack of Ragnar. Use Can I Idle to check if you can do it. You want to be able to tank everything else to reduce the chance of death.
The spell of choice is either 20k-accuracy Slicing Winds or Gust if you unlocked it. With them, you don't have to worry about the long fights because these spells won't miss if they're fired at accuracy of 20k or higher.
Having Finn, the Cat does not make a difference for the following, coincidentally, and thus could replace the need for the last HP level.
Extra DR
An Earth Layered Shield (ELS) is better than a Dragonfire Shield (DFS), but is arguably harder to get. The ELS requires a total of 64% DR, the DFS requires a total of 62% DR.
Note that the ELS gives 4% extra DR by itself, effectively reducing the extra requirement.
You can get up to 1100 hp through agility, reducing the total dr% requirement with Wasteful Ring to 56% (the -2% dr one is not worth it). Without Wasteful Ring, get it up to 1120 HP at the cost of two DR%, and you will only need 64% dr.
AS MAGIC, At 1000 HP, and without Wasteful Ring, you would need 71% DR.
AS MAGIC, At 1030 HP, and without Wasteful Ring, you would need 70% DR.
Maximized Farming
The rest of this guide is NOT for your first clear, your average clear, or even your first 100 clears. This is purely to maximize scrolls for any missing items. This will assume 99 in all skills, access to nearly all weapons and items in the game, and access to all DR and HP pets. This assumes you are (unless otherwise noted) using an optimal Agility setup, are using your best dps prayers, your best summoning synergy, and are using Diamond Luck Potions
Ranged
This build runs a fine line between alive and dead, tradeoffs may be necessary for your setup to survive.
Cape of Prat is marginally faster than Maximum Skillcape, but as it more than doubles your ammo expenditure, it is not recommended.
This clocks in around 19 to 20 scrolls per hour, depending slightly on your Astrology bonuses