http://www.bls.gov/oco/ocos069.htm

What subject do you want to teacher. Usually it will line up like this. Chose one and study really hard on it.

Math

General Science

Chemistry

Biology

History

Economics

English

Foreign Langauges

Vocation (Elective)

Almost always you need to be certified. Each states is slightly different. Some are even the same as others. Your probaly need to major in the subject you want to teach and take a lot of Education coarse.

http://www.uky.edu/Education/TEP/usacert.html

Lets say you dont want to study math but you still want become a math teacher. Fortunately, secondary teacher suffered a shortage and introduced an alternative certification.

http://www.teach-now.org/

https://www.teachforamerica.org/admissions/how_to_apply/requirements.htm

http://www.indiana.edu/~acp/program/acceptance.shtml