Class 11 and 12 is the most important phase for your carrer. Taking Physics, Chemistry, Mathematics as core subjects you can opt for Biology as the elective subject which will help you in making a great career ahead.
After concentrating for XIIth, you can apply for various medical level examinations like AIPMT, AFMC,AIIMS which has excellent opportunities in the field of medicine and health.
If there is any hesitation for Biology, you can opt for IIT-JEE, AIEEE for which you can go for Engineering studies that has good opportunities for a particular field in Engineering departments.
IAS is very different subject from Engeneering and Medical fields which will give a position in Goverenment sector. If yoy are going for simple graduation, you can concentrate on Indian Administrative Service(IAS) and Indian Forest Service(IFS) which will give you a better carrer ahead.
Go ahead and set your own goal!!
BEST OF LUCK...