0Lines or contour drawings are a good preliminary way to capture what you see and your own interpretation of it. However If you are into realism , you would need the value planes and light play as the first stepping stone to adding volume into your sketches .
One way to learn value planes in a setting ithe good old age "squintting!!" . Look at a subject and look at it again squintting your eyes . As much so that the details and colors dissolve to give you a minimum value planes . Most of the times figuring out three values i.e. Light , Dark and medium values gives good information on paper or canvas about the setting .
Another way to do it is photographing the image , increasing the contrast and coverting this output in a black and white picture. This however should only be used as a part of practice and not the mode to paint or sketch all the work you are going to do . Evenyually you would want to learn to convert the visual information you get from a real life subject on to the paper or canvas just by squintting your eyes. Sketch as much as you can from real life , there is no necessity to copy someones process or work unless interested. For your own expression to come through it is vital that the a personal approach to deiphering sight is figured out through practice.
Keept sketching keep painting
