Aspiring IAS career while studying 11th standard itself, is appreciable. That means you have a clarity on your future. Quite good.
As far as basic information is concerned, our seniors have already briefed you. To become an IAS officer, you have to be top in the civil services examination which is conducted by the Union Public Service Commission. Civil Services Examination consists of IPS, IFS and other allied services alongwith IAS on top. As our Partha sir said, optional subjects have to be selected properly in which you are most confident and comfortable else you will be in trouble. General studies also play a pivotal role in clearing the exam.
For preparation, apart from mastering in your present studies, you have to habituate in referring all kinds of competitive exams magazines, Reading of daily newspaper (preferably The HINDU) and for general studies NCERT books of social, science from 6th to 10th standard. If you cater certain time exclusively for your goal apart from routine study, you dont need to have a coaching. Cracking in first attempt is also possible.
All the best my dear.