You are on the right path if you are deciding to get into central government college for pursuing B.Tech course after the 12th Class. For your kind information all admissions to IIT's, NIT's, IIIT's and CFTI's (Central Funded Technical Institutions) are done on the basis of Rank scored in JEE (Joint Entrance Examination) Mains Paper - I. For being eligible to appear for JEE Mains you should score minimum 75% in Class 12th Examinations. In JEE MAINS too you should score a valid rank i.e. upto 50,000 to get into a good government college. So you should start preparing accordingly.

All the very best to you ! Hope you get into a good College.