I will try to answer this question keeping in mind my experience of 7 years of teaching medical students for various entrance examination. I think medical students should follow this broad regime-
First prof- One should not even think about PG entrance exam in the first year. One should try to read standard books in the first year. Cramming the short cut notes or books (kunjis) should be avoided. The simple reason being that 1st year kind of sets the tone for the rest of the MBBS. Try to be a good student in the first year, the likelihood is that you will remain a good student for the rest of MBBS.
Second Prof- Second Prof is very crucial. But you should go easy in the first 6 months. Have fun, attend college festivals, do some extra curricular activity. Basically do something beyond studies. In the remaining time of Second Prof, ensure that you study Robbins Pathology as nicely as possible. It will help you immensely during your final year and also the entrance examination. Apart from pathology, pharmacology too is quite important. But again, no need to do any MCQs or prepare for NEET PG per se.
Third prof- Now you are in the clinical prof. And its time to get serious..But before you get serious ,the beginning of the third prof- again deserves some fun time.
Reason — This is the last time in your medical career when you can relax for a prolonged period of time. After this , the next time you will get to chill for a significant period of time , would be during your honeymoon . So the first three months take it easy.
After that the serious business should begin. You should aim to finish at least 2–3 systems of medicine (say cardio, respi and GI) and 1 or 2 short subjects (say psychiatry and derma, or at least one of them) during the third prof. Ofcourse you need to study ophtha, ENT and most importantly PSM. In the third prof, you should start looking at MCQs. And ideally third prof is the time, when you should consider joining one of the coaching institutes. Although, I must stress upon the fact that joining institutes is not compulsory at all. A large number of students don’t take any coaching but still do very well.