Pretty decent start. You should post questions like this in either the stupid question thread, or the WIP thread. There's much to tell you. But for now, I suggest modelling the whole head. Not only the face. Because you need to see how the face looks while stretched over a skull. Figuratively speaking, you don't have to import an actual skull. Just imagine the shape in your mind. You can easily make the back of the head by selecting the back edges and extruding them back. Then closing them in the back.
The way you're making the face currently, it's flat like a mask. Because you're not building it around a skull.