What is the best technique for drawing diagrams in an exam?

First, list all the information you need to include as a reminder in some spare space. For example, if you had to draw a plant cell writing "cell membrane, cytoplasm, nucleus, mitochondria, ribosomes, vacuole, cell wall, chloroplasts", this will help you remember to include all of the information for full marks, and also help you label your diagram.

Sketch out your diagram in pencil first. If you have to finish the exam in pen, still draw in pencil first, then fill your diagram in with pen when you are confident with your drawing. This makes it easier to correct mistakes.

Remember to use a ruler for straight lines, particularly if you are drawing a graph.