Some tips for pencil sketching a tree include beginning loosely sketching the shape of the entire tree and working with simple lines. Observe trees in winter to understand their basic structure, and sketch on sunny days to best see light and shadow.
Sketch trees rapidly without worrying about being completely accurate. Focus on generalities like main branches and general leaf shapes to capture your viewer's attention. Squint your eyes so you can see masses of light and dark and not get overly involved in small details. Start from the bottom, and sketch the tree the way it grows. Pay close attention to the trunk so the roots look like they are growing in the ground and do not look cut off like a log.
To sketch a group of trees, look for lighter trees next to darker ones so they don't meld together in the drawing. If sketching with colored pencil, pay close to the greens, yellows and browns in the different trees. To make a tree look like it is fading in the distance, soften the leaves at the outer edges of the tree canopy. Experiment with the same tree in different compositions or with textured paper and techniques such cross hatching.