It depends on the level of knowledge you have on the subject. If a student lacks in Maths, then they should attempt more papers in order to revise more on the topics. But in general, 7 to 10 sample papers is recommended.  It is important to solve at least one paper a day after completing the syllabus. Maintain a stipulated time schedule and finish the papers in a given time. It is better to solve on a daily basis than all at a time.