Heidelberg University (Germany)

I'd like to congratulate you. You are already ahead of many of your competitors by starting in 12th. A few things you should know beforehand –
The competition is VERY high. You have to be in the top 99.5 percentile to get into a government college. If you're like most people, you wouldn't want to take a drop, so I'd suggest that you keep a backup plan. Prepare well for boards too. You should start off by knowing about the exam and it's marking scheme first. 180 questions, +4 for every right answer, -1 for every wrong answer.
Total marks: 720. You should aim for 600+. It has 45 questions of physics and chemistry each, and 90 questions of biology. For biology, you have to master NCERT. You should literally know every line of the 11th and 12th biology NCERT by heart. Once you have done that, you can move on to your coaching books and notes. Aim for 320+ marks in biology. Chemistry
Physical and organic chemistry is all about knowing the concepts and solving as many MCQ's as you can. Reading only NCERT will not do. Inorganic chemistry can be studied directly from NCERT, no need to cram any high level coaching stuff. Aim for 150+ marks in chemistry. Physics is the subject which differentiates between the good and the exceptional student. Devote atleast 40% of your time to physics. It will help if you have taken maths as your 5th subject. If not, you should get a tutor to teach you basic calculus which will come in handy for physics. I personally suggest that you solve HC Verma. It's a tough book, I know, but it builds a strong base. You can solve your MCQ's with ease after you've done HCV. Aim for 140+ marks in physics. I will also advice you to take some form of coaching. If not classroom coaching, you can take a distance learning programme. You could also purchase an Aakash Itutor. The coaching you will take will also provide you with regular tests, which will tell you where you stand, so you can modify your studying strategies accordingly.