There are many options available for you after doing your B.Tech in mechanical engineering it totally depends on your interest what you prefer if you want you can go for job in private as well as public sector.You can go for higher studies. You can appear for GATE exam. You can also go for diploma courses.

If you have interest in management field you can go for MBA.

For engineering graduates, there is the IES in addition to the civil services one. If you feel that a government job will provide you with much better facilities and a safeguarded future, then start preparing for the civil service examinations.

You can join the Indian Army/Navy/Air Force or any other wing. Apply for AFCAT (Air Force Common Admission Test).

Good Luck!!