If you were aiming for UPSC then you must have start earlier but still you have few more time left to prepare for UPSC. You should start your preparation as early as possible. As UPSC has a vast syllabus, first you should break it in few segments. Here a planned study time table will help you a lot. Ignoring even a small chapter can cost a lot. So you should focus on completing the entire syllabus. For Prelims, you don't need to go for deep understanding. Covering the syllabus from simple books will be great. NCERTs have been the best books for UPSC Prelims over the years. Keep the deadlines in mind and prepare accordingly. Revision is a must thing. Also solve previous years papers to understand the exam pattern and the types of questions.