As a GM I'd like to feel like I fully understand how to utilize my monsters tactically, but over the past couple months as I've been running the beginner box and now leading into Abomination Vaults, I feel as though I'm very often just making three strikes with an enemy or moving and striking twice unless the enemy has a very specific action in its statblock which is obviously better. Like a dragon is obviously supposed to use its breath weapon, but then I ran goblin warriors last night and I couldn't even figure out how to use their scurry reaction beneficially.
Intelligent monsters will act intelligently and go after the most immediate threats to their safety first , they will be worried about the archers and mages in the back line , and they will try to coordinate their group to keep the melee enemies engaged with their melee units while their ranged units attack their enemies ranged units. Or they will use ambushes to deal with these threats first.
Animal monsters will simply engage the closest enemy and attack and retreat if they are injured.