Class 12-science

I would suggest, don't decide on any AI area until now. You have so many years ahead of you. So welcome all AI topics. Learn, exercise and explore everything you find interesting. After 3 or 4 years (until final year at college) you might find your heart racing for one domain more than others. After that you should decide your field. Do your final year's project on that. Make sure you choose your dream project pretty challenging and start 6 months ahead of what your college prescribes/advices for final year projects.
First be strong in your logic. Which means you should have more than 1 or 2 tool (s) to solve your problem. By tools here I meant mathematics. Concentrate on Linear Algebra and Calculus. One of my professors used to say "Anything and everything is linear algebra. Give me any problem in any domain, I will use LA to solve it". Mind that he is a multi-disciplinary professor and he means it.Statistics, probability theory and graphical models - These are the fundamentals for modeling your problem and doing inference from models. So now you have got tools to solve them, but how will you express them to the computer/machine? Be strong in any 1 language, preferably C+ or Java. Python is a boon if you can learn it. Then to advance further, learn some functional programming languages to scale in distributed environments. See linear and functional programming/quadratic programming series from Coursera.
Intake up /prepare for competitive programming like ICPC, google summer of code, etc. More problems you are exposed to better will your analytic and logical skills get (I never did this in spite of having a fetish for programming, I regret this a lot). It's time you start doing some MOOCs. For any AI task ML is important. So do 3 courses from different professors. The reason is that each one will have a unique new approach towards teaching ML. Learn all flavors of ML then move on to narrowing down where you want to apply your ML and do further study/course on the narrowed down field, maybe NLP, speech, vision, robotics, etc. Choose top journals from your area of interest and keep reading papers from them regularly. This way you can keep track of where the area is marching and state of arts.