I don't plan it out persay , I tend to just build all the loops in as I go, the topology does differ slightly from model to model , depending on how detailed the face is or how high or low poly it's going to be, I tend to build the face in a specific way, so I'll start with disk, with the centres removed for the eye sockets , and make sure these have the desired loops , same for the nose and mouth areas , once you've got all those made its just a matter of connecting them altogether, I know that Its impossible to avoid 5 sided poles so I'll just make sure i put these as far away from the mouth or any area that's going to deform as possible, sometimes I'll come back to it later on and adjust the topology if I can see a better way of doing it that I didn't spot the first time, it's sort of like a puzzle every time but after you've built a few characters you can kind of visualise the topology and where to put this and that before you've even got to that part.