The basic criteria of eligibility is (10+2) or equivalent qualification with Physics, Chemistry and Biology and/ or Math as main subjects and a min score of 55%. Admission In reputed institutes is usually through entrance exam whereas in other institutes you can take direct admission. I am enlisting a few good colleges which are doing really well in this field and are known for their quality education and better placements. Top colleges are:

Gujarat Forensic Sciences University, All India Institute of Medical Sciences
Lok Nayak Jayaprakash Narayan National Institute of Criminology & Forensic Science, 
Lovely Professional University Jalandhar, 
Jawaharlal Nehru Medical College, 
Dr Bhim Rao Ambedkar University Agra, 
IFS Nagpur, Pune, Aurangabad, 
Osmania University Hyderabad.

To get admission in B.Sc Forensic Science one should have completed 12th with PCM/ PCB. However to pursue B.Sc Physics, Chemistry & Forensic Science one must have done 12+2 with PCM subjects. Whereas to pursue B.Sc Life Sciences , Chemistry & Forensic sciences one should have studied PCB/ PCMB.