I’m going to start with lower-level monsters and work my way up, and my first case study will be the monster that players beginning with the Dungeons & Dragons fifth edition starter set are likely to encounter first: goblins.
Here’s what we know about goblins from the Monster Manual: First, from the flavor text, they live in dark, dismal settings; congregate in large numbers; and employ alarms and traps. They’re low-Strength and high-Dexterity, with a very good Stealth modifier. Their Intelligence and Wisdom are in the average range. They possess darkvision and the Nimble Escape feature, which allows them to Disengage or Hide as a bonus action—very important to their action economy.
Because of their darkvision, goblins will frequently attack under cover of darkness, when their targets may be effectively blinded (attack rolls against a blinded creature have advantage, while the blinded creature’s attack rolls have disadvantage). They’ll also attack from hiding as much as possible, making use of their high Stealth modifier, and doing so in dim light decreases the likelihood that they’ll be discovered, since
the many player characters will have disadvantage on Perception checks that rely on sight. (Important note for dungeon masters and players: Darkvision does not nullify the penalty to sight-based Perception checks in dim light. It only lets a creature see in darkness as if it were dim light, without being effectively blinded.) (The description of darkvision on pages 183–85 of the Players’ Handbook is incomplete: it implies that darkvision improves vision only in darkness. It improves vision in dim light as well, allowing a character with that feature to see without penalty.)
A picture of goblin combat is starting to coalesce, and at the center of it is a strategy of ambush.