How to think about head construction
The eye sockets are an incredibly important part of head construction, and often students will draw them too small, or without enough care to properly reflect this.
The cranial ball we start with is a rounded, smooth surface. Heads, however - regardless of species, with humans included - are actually a combination of flatter planes. The trick to head construction is figuring out how to build up to the correct arrangement of flat planes. Figuring out where to actually draw the edges between them.
The eye sockets are our first introduction to straight(-ish) edges, taking an otherwise rounded ball and laying the groundwork for separating it into a series of planes. Once in place, we can start connecting the other facial elements to it - a footprint for the muzzle, which can then be extruded out, as well as the brow ridge and the cheekbones.
All these pieces fit snugly to one another, rather than floating loosely without any clear relationships. The head is a three dimensional puzzle, and once completed, you can think of each of these forms as chunks that fit perfectly into one another, all buttressing around the eye socket.