One can create outlines in a lighter shade or heavier, based on their preference. The pressure on the pencil brings out the lighter or the heavier ones.
The lighter outline can be created both using a ruler and just in a free-hand style. While doing so, you must reduce the pressure applied onto the paper and hold the pencil at an angle less than 60 degrees, so that the pencil moves in the direction that you hold and pulling from there.
Heavier outlines are done mostly at the end, to provide a highlighting effect. It’s mostly done using freehand style. By simply adding some pressure on the pencil, the effect is seen. The pencil grip should be firm and held closer at the nib.
This is a technique that uses small lines or dots that are placed just little apart. This one is very useful for blending purposes, created with light pressure. For example, while drawing the iris of an eye, you can use this method and find it done at perfection.
This is another technique that is done by marking out small lines clubbed together, to create or fill colours. This is mainly used for shading effects, and just like the outlines, it can be made lighter or heavier with changes to the pressure given.
This is a process very similar to the hatching process, but the only exception being that another layer drawn on top of the first layer in the opposite direction. It almost forms like a mesh sort of structure.
You can use this for shading purposes, by adding more layers you can give a darker shade to the portrait that you are working on.
These are used by professionals and the budding artists in equal ways. It adds or brings a life to the image, by highlighting them. it gives a new dimension to the image at the end. You can make it lighter or even darker based on the area and the image you want to highlight and make it look real.
This technique uses a circular motion of drawing, keeping them all compact, to keep the shading close and tight. You can use this technique for blending purposes and shading, getting a smoother texture of the image.