This depends on how well you want to perform in your exams. If your aim is to just get passing marks, then it is fine to prepare from the last 5 years' question papers. But it also depends on luck as sometimes all the questions are new and none of them are repeated.
Therefore it is better to study everything and complete the syllabus and then practice from the last 5 years' question papers.
Try taking the guidance provided by your teachers and also your seniors. You can opt for coaching classes also to prepare better. Divide your strengths and weaknesses and work on them accordingly.
Lastly, practice from the previous years papers. This will familiarize you with the question pattern, the overall questions and give you an idea about the time limit.
The previous year's examination question papers of Aligarh Muslim University can not be found on the internet. The main reason behind that is AMU does not make their paper public.
If you want the previous year's papers, contact the members of the seminar library of the AMU chemistry department. Or else you can check the Maulana Azad Library about the previous year's papers of MSc. If you know any research scholars in the department, they might help you. Moreover, in Aligarh, there is a Shamshad market, famous for bookstores. You can buy reference books, previous year papers, etc. from the bookstores there.
There is usually no need to look for SHUATS old entrance exam papers as it is quite easy. If you have a general idea of school level Mathematics, Physics, and Chemistry, it will be easier for you.
Brush up on current affairs and GK, just to be completely prepared. Students of ICSE and CBSE boards will find the exam to be very easy and in their grasp.
The competition in SHUATS is very little, which is an advantage. Make sure to attempt all the questions as there is no negative marking. The exam has a total of 60 questions on Aptitude and 30 questions on Physics, Chemistry, Maths/ Biology.
There are various options for online mock test series for practicing the BITSAT test papers. In the following, some of them are discussed.
MyPAT:
Embibe:
TCY Online:
Keeping in mind the above considerations, it can be stated that MyPAT is the best to practice mock series for BITSAT test preparation.