Before starting the retopology, I’ve made a bit of a research. I found a good tutorial on the 3DArtist website by Steve Holmes on the subject (in references). I also had a look at a few videos on the plurarsight website. I’ve seen everywhere that it is important to pay attention to how the muscles work on the face.
With my first try on retopologizing the done head model I made a few mistakes. First, I started out with too small polygons which made my work much harder. After a while because I made a lot of mistakes in the edgeflow as well I decided to start over.
This is my messed up mesh. I felt like I was starting to get the hang of it now, so I hope the second one will be better.