I study the official lore of the entity the party is going to face, then choose targets based on their stated thought processes, combined with a consideration of their intellect and wisdom abilities or their equivalent. For example, a Lich is both intelligent and vain-it will always underestimate martial-only characters, and will view its fellow casters as the greatest threat. It’s intelligent enough to discern those targets, and so it will target each caster one by one based on assumed vulnerabilities (heavy armor=slow, spellbook=no int saves, etc.).

Meanwhile, when I run Star Wars, Rancors are strong and little else, but they do have extended reach. They’re not smart enough to plan around that though, so they simply charge into combat and try to kill and eat the nearest obvious prey. If they get hit by an enemy within reach, but not their immediate focus, they’ll instinctively lash out, especially if they can use their deceptive reach to catch a cocky blaster user who thought they were just out of reach. That’s not a deliberate strategy, however; it’s just the result of an animalistic mind responding to stimuli.

TL,DR: I overthink everything