I prefer behavior trees over state machines, a slightly different theory, and imo more flexible. there are no exact standards, but e.g. the one in unreal engine 4 is quite good, it is an event driven approach. currently I'm working with it in a FPS/RTS game project and really like it. there are many examples for simple FPS enemy behaviors, and these can be implemented in lite-c too, relatively easily, I did it earlier for my RTS project. together with a good pathfinder (a navmesh is usually fine) AI creation has never been easier.