Test preparation

Hi Arindam,
If you are in class 11th, prepare either for SAT or ACT and IELTS or TOEFL. You need not take GRE (which is taken for Masters in USA). You must register yourself on the official websites of the respective test administrators, create an account and schedule a test date. You will find information on syllabus, test format and online test prep materials too.
Here are the webpages
SAT
https://collegereadiness.collegeboard.org/https://collegereadiness.collegeboard.org/
ACT
http://www.act.org/content/act/en/products-and-services/the-act.html
IELTS- British Council
https://www.britishcouncil.in/exam/ielts
TOEFL
https://collegereadiness.collegeboard.org/https://collegereadiness.collegeboard.org/3
Good Luck.

Concentrate more on general aptitude, this will be quite easy to score more. Don't stuck with the unknown questions and concepts, have a look on almost all categories of question paper and choose the section that you will excel. Practice more with the solved and previous, year question paper. How to Crack GATE Chemical Engineering. Prepare a quick guide and make note of each chemical formula and equations that you are learning. This will help you to give a fast look on formulas during exam time. No need to search for formula on various pages. Have a regular read out on every concept and work out more than analyzing the concept. Score more with some online tutors and mock test practices.

Dear Anant, first of all I am happy that you have a clear picture of what you have to do. Secondly, now when you have decided about your ambition, it is advisable to first completely concentrate on your 12th board. This is your first lesson for a step towards bright future. The efforts that you put must be such that you should be able to excel in your 12th. However, simultaneously develop a habit of reading newspapers, magazines and watch news channels. Be aware about what is happening in the country as well as on international level. Try avoid reading material that is not relevant for you. You must always know, " What not to read". Prepare your general studies as it is the only subject which takes time to develop an understanding. Once you clear your 12th, than go for further preparation along with your graduation. Your 12th will serve as a platform for your future studies. We can surely guide you about your future once you clear your 12th. I hope this would suffice.