While drawing one needs to observe the subject, draw it with perfect proportions, and maintain good clean lines. However, shading with a pencil gives you more freedom and ease, as one doesn't need to be confined to perfect proportions, but just needs to take care to catch the light and shadows falling on a subject well. So, first learn to draw your subject well, and then learn how to use colored pencils to complete your artwork.
Before I start explaining about the different shading techniques used for texturing, let us discuss the lights and shadows that gives all the objects their depth and form. While shading any object, it is important to observe the subject, to figure out the three main parts- highlight, tones, and cast shadow. The image below shows the light source on top right corner, highlight, shading of mid tone and dark tone, and the sphere's cast shadow. Understanding this and by practicing the shading and texturing techniques mentioned below you can draw detailed colored pencil art. However, practice observing the highlights, tones, and cast shadow of different objects. Pick simple objects on your desk, and dissect the lights and shadows falling on the object.
Similar to the above technique, in this technique you can merge two or more shades together. You can increase or decrease the pressure on the pencil to get a lighter or darker shade of the desired merged color.
Again use a pencil which has a fine tip for this technique. Make a patch with angled strokes, then overlap a patch of another opposite angled strokes on the first patch. This technique greatly helps to add depth to areas which have shadows. The cast shadow in the first image is created using this technique.
Similar to the above technique, all you have to do is use two or more colored pencils. For example, you can use shades of green and brown to create a shadow of a tree on the ground.
Stippling & Shading
Stippling can be done with pencils, but is mostly done with felt tip pens as they have perfect pointed edges. Use a sharp tipped pencil and hold it perpendicular to the paper, and increase and decrease the pressure to create this stippling effect. It can be used to create textures like showing leaves on a tree, or for shading a drawing subject like a portrait. In the picture, I have illustrated the light, middle, and the dark tone which can be created using stippling.
Razor to Lighten Shade
These colored pencil tips are greatly helpful for corrections. If you think you have made a patch that is too dark, then just scribble with a razor and then smudge the patch to make it look smooth. This technique shouldn't be tried on a thin paper, as there is a possibility of the paper being torn. In the image I have used a razor on the top part of the patch, and left the bottom dark for you to study.
Using a razor to make incised marks helps to expose the color layer beneath the top color layer. In this picture the bottom layer is green and top layer is red. Then using a tip of a cutter, some incision marks are made in the middle of the patch to display the green colored layer underneath.
Learning to paint with watercolors is a task that needs more skills, compared to shading, which is an easy task. However, you can use water soluble pencils for shading and then run a wet brush to give the water color effect. In the image above, I have used Staedtler Luna watercolor pencils, and then used a brush lightly, which gave the color patch the water color effect.
Draw simple subjects, and use the above techniques for texturing and shading, to create detailed looking pencil art works.