1) Running behind tons of subject-wise compilations flooded in the market 30 days before exam. Please don’t do that. Trust your preparation till now. 90% of the data in it would have already been covered by a serious candidate beforehand or would contain information-overdose. Don't stress yourself by doing so. 2) It is not recommended for one to do mock tests till the last day as if one test does not go well for you, it might stress you more. So, make sure you are just revising your notes a few days before the test and relaxing your brain for the test day. 3) Focusing only on a few topics you believe are ‘important’ is one common mistake candidates tend to make. We can never predict which route UPSC might choose this time, so spread your time proportionally with current affairs being a common theme. 4) Conversations with other candidates before exam and talking of attempts and preparation should be avoided. Prelims is much a matter of mental grit and holding your nerves, don’t let any external factor play a role. 5) Be wise while attempting questions and remember that there is negative marking. Don't get overconfident during the exam that you forget about the negative marking. 6) Another common mistake is ignoring Paper II. Do take a few tests to make sure everything is sorted at this end. 33% is really easy to get, provided you know what the paper is about. Hope this helps!