Not only practising previous year's question papers , but also you should study NCERTs properly. Concepts given in the NCERT textbooks are very helpful in cracking difficult problems asked in competitive exams. Beside NCERTs, you can also refer to other books like HC Verma for Physics, Organic Chemistry by O P Tandon, Concise Inorganic Chemistry by J D Lee,  Objective Mathematics by RD Sharma etc. You should also focus on your accuracy to avoid Negative marking.