Practice papers are most useful when they diagnose what to do next. Work under sensible time pressure, show your method clearly, then use the solutions to separate slips from genuine gaps in understanding. Return to the relevant Learn and Practice material before trying another mixed paper.
Attempt
Work through the paper without looking at solutions. Show enough working that you can later see exactly where your reasoning changed direction.
Check
Mark method as well as answers. A wrong final answer can still contain good mathematics; a correct answer can sometimes hide an unreliable method.
Target
Turn errors into a short revision list. Relearn weak methods, practise them by topic and then return to mixed questions to test whether the improvement holds.
Exam approach
Treat a practice paper as feedback, not just a score. Record which topics cost marks, whether the issue was knowledge, method selection, algebra, interpretation or time, and use that diagnosis to choose the next piece of revision.