As such there is not much difference between preparation strategy for IAS Prelims and Mains exam. The only difference is answer writing techniques as Mains exam is more about essay type answers where you need to present your ideas and thoughts wisely to impress the person checking your paper. Time- management, dedication, test-series and practice remain the integral part of IAS mains exam preparation.
As far as books, syllabus and test series are concerned, it is better to take admission in a coaching center that offers right guidance. One of my friends attended Vajiram and Ravi for IAS Mains Exam preparation and liked their strategies a lot. The faculty at the institute offers updated syllabus books; conduct mock test and advice students with the tips to perform well in the exam. Further, they also offer handmade notes to help you utilize your time on studying other important books.
Just make sure that you practice answer writing as much as you can to write the best answer in limited time. Make your answers impressive with bullet points, headings, sub-headings and graphs. Try to explain more in limited words and keep your points in easy to understand language.
Wish you all the best in advance!