The basic rules to be a Higher Secondary school teacher is that you should be a PG with a B.Ed degree.

So the process is:

• After 12 pursue a course for UG.
• After completion of UG go for BEd or PG. If you complete PG after that you can also apply for BEd. Also there are some colleges that offers intergrated BA-Bed/BSc-Bed/Bcom-Bed courses. If you enroll in that then also you will be prepared to be a teacher in a school.
• Now you have to go for the government school service  exams as organized by different state government. On qualifying the exam you will be called for an Interview. As the Interview is over you will get the scope to be a government school teacher.

So this is the procedure for being a school teacher in government schools.

I hope my answer helps. All the very best for your future endeavors!