see; do not simply copy a stylized textbook illustration. Suppose, for instance, you wish to draw a cross-section of a Smilax root from a microscope slide (see Fig. 9.1 and the sample student drawings based on it in Fig. 9.2). You need not be an artist to render an accurate, detailed, and comprehensible illustration. Use pencil for your initial sketch and allow enough room to include sufficient detail. Label your diagram carefully and always print legibly; be sure to identify details using the correct terminology. Check that all lines pointing to particular structures are drawn unambiguously. Provide a legend so that you know exactly what is being represented; note the magnification for microscope drawings.
This was taken from the 4th edition of Writing Papers in the Biological Sciences by Victoria E. McMillan