When sketching in pencil, use different levels of pressure to create different effects, and use direction when making marks to direct the viewer's eyes. Choose the right paper and pencil for the drawing, as these have significant effects on the drawing quality.
The amount of pressure you apply to the pencil while drawing determines the appearance of the line. Changing the pressure creates contrast in the lines. One way to create a line that appears fluffy is slightly lifting the pencil towards the end of the line.
By using controlled lines that follow a set direction, you define what you're drawing. For example, contrasting directions create an edge.
Drawing papers work most effectively for sketching. Certain pencils are difficult to use when drawing. Hard grade pencils tend to be better, although it depends on the type of drawing.