I’ve become a big fan on having a pre-set script of attacks and actions that a major enemy will take, given that most combats in D&D last 3 rounds. Generally that means they’ll get their biggest spells or attacks out first, they’ll use legendary actions if they have them, and if they’re still alive by round 3 and assuming they’re seriously hurt, they’ll be looking for their escape. In short, I want to take me as an active combatant out of the equation and put myself in an adjudicator role while still not underselling what the enemy can do.