Write the introduction, abstract and conclusions last

The introduction and abstract describe the whole project, so they are easiest to write once the rest exists. Draft them early if you like, but rewrite them at the end.

• Abstract: a short, self-contained summary of the problem, what you did, the key result and what it means. FAST's handbook describes it as 50 to 125 words that state purpose, findings and conclusions without evaluating the work. Check your own limit.
• Introduction: the problem, why it matters, your objectives and a one-paragraph map of the chapters that follow.
• Conclusions: what you achieved against each objective, the main limitations and sensible future work.

Readers, including examiners, often read the abstract, introduction and conclusions first. Make sure they agree with each other and with the results chapter.