Past papers are published for IGCSE subjects and are the closest thing to seeing the exam before sitting it.
Start topic by topic
Waiting until the syllabus is finished wastes most of the year. As each topic is taught, the past questions on that topic can be answered immediately.
This also teaches the question style early, so the final months are revision rather than a first encounter with the format.
The mark scheme is the real document
The paper shows what is asked. The mark scheme shows what is rewarded, and the two are not the same.
Mark schemes often require specific wording. Two students with the same understanding can write different sentences, and only one of them scores. Learning the phrasing that earns the mark is a substantial part of the grade in the sciences.
The examiner report
Published alongside many papers, and read by almost nobody. It states what candidates did well, what they got wrong, and which misconceptions recurred.
It is the only document that tells you in advance where most students lose marks. Reading it for the last two sessions before an exam is a short task with a large return.
Timed full papers
Saved for the final months, and answered under real conditions: no notes, correct duration, no pauses.
A paper answered with the book open measures nothing except whether the book contains the answer.
Watch the syllabus version
Syllabuses are revised. A past paper from an older version may test content that has been removed or use a structure that has changed.
The syllabus code and year should be checked before a paper is used, and the current syllabus is published by the board.