Again, lines and shapes divide spaces. Positive and negative space. Whether the space is black or white, positive or negative, depends on how you look at it. Negative and positive space are reciprocal of each other. You can apply this knowledge to digital corrections.
Biological samples display a lot of symmetry.
Think central symmetry when you have central structure and lines, and bilateral symmetry when lines develop from the central line outward. Avoid composition that separates the micrograph into two halves. It's better to tilt the bilateral line slightly or do a three quarter view. You want to record a full range of gray tones. Repetition and tonal value variation can cause excitement or agitation.