One thing I've learned in teaching my Realistic Drawing Workshops is that many pencil artists don't have a comprehensive plan when it comes to drawing a portrait. They're unclear about where to start, what to do next, and most importantly, how to determine the values they should be putting down on the paper when they begin shading.
These concepts are completely separate from drawing techniques, that have to do with which pencil to use where, how to shade, texture, etc. Having a great technique is useless if you don't know when or how to implement it. Without a plan, you can spend hours overworking areas of your drawing until you either damaged the paper or simply give up in frustration.
This 13 page guide has 11 photos that illustrate the same concepts I teach in my drawing workshops. These are the proven strategies that I train my students in so they can create a realistic portrait. The guide also includes a link to a video where I explain these steps needed to achieve realism in your portraits!