Well, I went to university without any clear ideas about what I wanted to study, so you're one step ahead of the game!
I discovered linguistics in my first year of university, and ended up majoring in it. After graduation, I worked as a linguist for a year at a software company developing English grammar-check software, then went to Japan to teach English for 3 years on and off. Along the way, I got my TESL (Teaching English as a 2nd Language) certification. After all that time, I decided to continue my linguistics education by pursuing a PhD. I am now in my 2nd year of the program.
Something to keep in mind is the difference between
Theoretical linguistics and
Applied linguistics.
Theoretical linguistics is the scientific study of the human language faculty. In other words, some questions linguists try to answer include:
What do all languages have in common? How do they differ? How is linguistic knowledge represented in the brain?
Subfields of theoretical linguistics include: Neurolinguistics (language and the brain), sociolinguistics, anthropological linguistics, phonetics (speech sounds), phonology (sound systems), morphology (word structure), syntax (sentence structure), semantics (meaning), pragmatics (meaning in context).
Applied linguistics in general refers to 2nd language teaching.
Linguistics is
NOT philology, study of grammar, writing style, literature, foreign languages, teaching of 1st language, and so on.
Many colleges offer courses in either applied or theoretical, but not both. Very often, applied linguistics will be offered through the faculty of Education, while theoretical linguistics tends to be in Humanities.
My advice would be not to limit yourself too early. Linguistics is a huge field with lots of fun stuff to explore. Apply to a college which offers a wide range of courses in things that interest you.
Another positive step would be to visit the local college library and browse through introductory textbooks in Linguistics, Sociolinguistics and Neurolinguistics. See what seems interesting and go from there.
Also check out the amazing resources on the web!
The following is a link to the Introduction to Linguistics course at my school:
Intro to Linguistics
Let me know if you'd like any more specific references!