I ran across this cool blog that talks about various monsters and their tactics, in context of who and what they are. Monsters aren’t deliberately dumb (though based on their Int they may be more or less sophisticated) and “blindly charge PCs till dead”, while popular among too many DMs, isn’t a really interesting or realistic set of tactics. So check it out and consider how everything from a razorvine to cosmic horrors would react to a threat.
Geek Speak
Geek Related 
I have been espousing the idea that monsters aren’t stupid and know what they are doing since 1976. The whole game of Monsters! Monsters! is built on that concept. However, their goals are very often incompatible with human goals.
It’s definitely a fun blog, and popular enough (in 5e circles) to have justified a nice hardback book.
We still play PF1 and 3.5 E but there still plenty of good ideas in there, to be sure