Past papers are most useful once you know enough of the course for your mistakes to tell you something useful. Before that point, selected questions from topics you have already learned can give cleaner practice.
As more of the course becomes secure, increase mixed questions, timed sections, and eventually full papers. After each attempt, study the pattern of mistakes and decide what needs repair before doing another paper. The score matters less than what the paper reveals about the next step.
Use the Examinations & Assessment Hub for paper strategy and the Study & Learning Methods Hub for revision planning.