Hatching is a great way to create value with both pen and unblended pencil. Here are a few variations of fast and effective hatching technique.
Make sets if tiny overlapping circles or squiggles. This creates a rough, loose organic texture. To darken, and more squiggles over the squiggles. Blur your eyes to find areas of uneven value and fill these with additional marks.
You can use parallel lines to fill an area with tone. By varying the spacing and width (pressure) of the lines you can make areas darker or lighter. Use your non-photo blue pencil to add a few parallel lines before you start to help prevent your lines from drifting to a new angle across the hatched area.
If it will take multiple strokes to make a longer line, try leaving little irregular spaced gaps between one line and the next instead of overlapping the strokes. Overlap strokes often make irregular blotches while irregular spaced gaps add a little sparkle to your technique.
If your lines show through in your final drawing, their direction can help to show changes in the planes of the object you are drawing. See Showing Planes with Line Angle. Alternatively, you can keep the line direction consistent across planes, reducing detail in the shaded area and allowing it to recede into the background.
People see bold and widely spaced lines as “lines”. If you make the lines lighter and closer together, you can achieve the same value and people will ignore the “lines” and read them as an area of tone.
Can’t draw a straight line? Patch hatching is for you. This technique is very vast and creates a dynamic and interesting texture. Create small sets of interlocking lines, varying the angle of each set.
Cross hatching is a fundamental technique to deepen values. There are a few subtleties with this technique that are often overlooked. The most important is to watch the angles of the cross lines, avoiding right, and sharply acute angles.
Instead of keeping the lines parallel, you can wrap them around a curved surface. As you draw, imagine the lines wrapping around the curved surface. The lines can fan out from a pinched shape to fill a larger area. As they do, the lines may become so spaced from one another that they no longer read as an area of tone but individual lines. Resolve this by making a second set of lines from the outside of the broad edge toward the narrow point. You can also cross hath these contour lines.