Prioritize Health and Damage
Going for a High Chaos run in Dishonored 2 basically means cutting down all enemies in sight. This also means that you’ll be getting into a lot of fights. To improve your survivability, I highly recommend increasing your health and damage output as much as possible. The Vitality ability and its upgrades will help greatly with your health regeneration and amount of damage taken. This is one of the first abilities you should definitely pick up.
Blood Thirst is an invaluable ability to have for High Chaos players as well. It essentially allows you to build up an Adrenaline meter as you fight enemies, and once the bar is filled up, you’ll get a free kill on the enemy you attack next. This allows for smoother combat situations, and can let you end fights much quicker than they would normally take.