Sketching in Photoshop has many advantages over natural media. For one thing, you can easily erase or adjust while sketching, and you end up with a composition that is, if not done, then almost.I sketch with a fairly big semi-soft brush (penpressure controlled size and opacity), and a big, rigid eraser (pen contr. size only). Brush foreground color is set to a warm mid-level brown, brush background color is set to the paper color (in this case white).If the sketch has several complex items, I usually work on them in separate layers, so I can easily erase overlapping objects. This image is fairly simple so it's all done on one layer. After sketching is done I resize, rotate and move some bits and pieces slightly with the Liquify tool.If I'm unsure of any proportions I might flip the image horizontally to check if anything looks odd, edit the odd part, and flip it back.After all this I flatten the image, and the "pencil-sketch" is done.