I think the best way to go about it is by drawing from photo reference first. Using your photo reference, start your drawing by sketching in the larger masses of the skull; a circle for the cranial mass and a rectangle for the jaw. Then, lay in your small masses such as nose placement ( about 3/4 from the top on the skull), eye placement (about halfway down the skull), the mouth placement ( between the nose placement and bottom of the jaw). Everyone's facial proportions are different. Theses placements are just skeletal markers that you expressions will be drawn on top of. They correspond to the bone structure your facial features are attached to.
The expression is drawn over these markers. Expression is muscle and dynamic! It can move about but stays around the bone structure it is attached to. For example, you smile and mouth muscles are pulled upward(dynamic)....but they are still attached to the bone of your upper jaw (static). Putting in these markers in first will help you keep the proportions of you face, making you face look more like the reference you are using. The more you practice from drawing reference, the more muscle memory you build, the easy drawing without reference becomes! All artists use photo reference and it is not something to shy away from. You can do it!