Drawing is an intimate caress filled with love. You are not copying, you are not tracing, you are gently exploring possibilities. Your pencil touch is light, it is an extension of your feelings, may they be of love, passion or anger. You are conveying the intangible. You are on a voyage of discovery. Your feelings and what you wish to draw may yet be unclear, your pencil is touching the paper here and there, spontaneously yet tentatively until the forms you are creating and what you wish to express become more clear.
You are drawing through a light fog until it is slowly lifted and you can see. Only then do you redraw each form. Light layers upon light layers until a sense of contrast arises to which you now introduce shadows. Decide on the general direction of light and of the shadows. They do not have to precisely correspond to the object or form that is casting them, be creative as you draw them, make them as elegant as the rest of your drawing. Make them follow the contour of the land.
It only matters that they are congruent and roughly follow the same direction and have the same length. Your entire drawing must espouse the same light. Do not worry about making your shadows perfect (it would require very complex spatial geometry to calculate them), instead make them look good, enough to fool the viewer’s eyes who is only likely to pay attention to the shadows if one of them looks horribly out of place.
Enjoy sketching and do not be in a hurry to fill your newly created forms with details, shading or colors. Erase, change, manipulate. You are creating something that no one in the history of the world has ever done. Let the tree that you draw become you and your unfolding waves an extension of you. Trust and decide that you are creating something beautiful, as unique as you.
If you are copying something, do not try so hard, instead inspire yourself from it. Let all you feel like an immense sea guiding its waves hold your pencil. Let your heart, not your mind compose your song. Make love to the paper and treat it like gold.