Here is some advice for describing a process diagram. The question I'm using comes from Cambridge IELTS 6. It's also on this website (go down the page to test 3).
- Introduction: paraphrase the question (one sentence).
- Summary paragraph: write how many steps there are. You could also mention the first step and the last step (two sentences).
- Details: describe each step in the diagrams.
Introduction and summary paragraphs:
The figures illustrate the stages in the life of a silkworm and the process of producing silk cloth.
There are four main stages in the life cycle of the silkworm, from eggs to adult moth. The process of silk cloth production involves six steps, from silkworm cocoon to silk material.