The document provides guidance on sketching for interface design. It discusses that sketching is not the same as drawing and outlines basic shapes and techniques to use like line thickness, size, shading, selective detail, and isolation. It also provides tips for sketching buttons, showing states, and headings and text. The document recommends exploratory sketching, sketchboards, and sketching individual components to explore design ideas. It lists useful sketching tools such as sharpies, brush tip markers, pens, pencils, templates, and markers.