Crosshatching is an effective way to create values with lifework. Here is an example of using this technique to suggest depth in a sketch of Yosemite Valley with a Bic ball-point pen. Click on the first image to start a step-by-step slide show.
Block in the positions of major features with a non-photo blue pencil, then lightly with a ball point pen. Start lightly the first lines on the page will most likely be the ones you will want to change the most down the line. As your drawing begins to take form, increase the pressure of your pen lines. Use a stronger line for foreground elements and let the pen work lighten up as you recede into the background. Add detail in the foreground mountains. Keep detail to a minimum on distant elements. Use contour shading to show the planes of the cliffs. Yosemite Valley runs East-West so the North-facing slope is in shadow while the South-facing slope is bathed in sunlight. Note how the pen strokes can suggest the planes of the rock faces. Lighten your strokes as you move to the background elements. Increase the contrast (difference between light and dark) in the foreground. Fill in the forest on the valley floor with fast hatched lines. Cross hatch the diagonal lines with vertical strokes to create shadows on the valley floor and to make the forest feel more like trees. Switch back and forth between this slide and the previous one to see the impact made by this simple step. Add a few foreground details and make final value adjustments. Remember to keep the strong contrast in the foreground elements.