In a 4 x 5 in. format, in your sketchbook, using graphite pencils draw a continuous field composition of a texture. Your image should only exhibit the details of the texture. This is basically a value assignment. In order to rendering texture in an interesting and believable way, the values must be fully developed.
Do not draw the shape of the object. The drawing above is a sponge and notice that the edges of the sponge are outside of the image area.