BITS pilani entrance has the same syllabus as JEE mains and for PCM one does not need a different preparation. The difference lies in type of questions asked which are relatively simple but more in number , so to score besides knowing the subject one should focus on accuracy .In Mains there are 25 question per subject to be answered in one hour .In contrast in BITSAT one gets roughly 50 minutes to solve 45 questions. Out of three hours I have removed 20 minutes for english and reasoning and 10 minutes for taking some bonus questions if you have to get score above 400.
One should take the NEET books of good publisher which have lots of questions per topic in physics and chemistry that way there will be many questions in paper that you would have already solved inpractice.
English and reasoning are to be prepared on long term basis rather than for specific exams .In life it always helps to have good vocabulary and general awareness of world around. Keeping them in syllabus BITS wants to ensure that they get young minds who are capable of thought rather than just byproducts of rote learning.
I personally suggest after class VI parents should buy their children a book by Norman Lewis ‘Word Power Made Easy ‘ that focuses on roots of words in English and encourage them to read newspapers .