I drew the portrait of Ian McKellen + Tutorial

Ian, she has a very expressive face. If you are just starting to make your first pencil portraits, I recommend you do it with people like that. With well-defined criteria.

It is essential, at least for the technique I use, to make a preliminary sketch. With a thinner pencil, then the shadows start to give it to you with a 2HB pencil. The pencil pressure against the blade will give us those results. It is also essential to start from left to right, if you are skillful, so that you do not drag the graphite with your hand and stain our leaf.

Digital retouching.

In this case, I just raised the contrast and a bit of the exposure with Photoshop. It's very easy. All you have to do is run tests until you reach the contrast you like.
You can also add light to the eyes, in the form of a reflection, only with white, you decide the intensity. In this case, I didn't apply it.