Reddit reviews Cinematography: Theory and Practice: Image Making for Cinematographers, Directors, and Videographers

Cinematography: Theory and Practice is great textbook.

Lots of people here are probably gonna recommend you Youtube video essays, but I'd recommend not wasting much time with them. They mostly bullshit and/or extremely superficial. Instead of those just watch great classic films.

And of course it's always great if you can shoot your own stuff and apply that theory to practice.

Check this book if you haven't already. Cinematography

this is a good book to start learning with

My advice would be to start where you're at right now. The internet is full of great websites and videos, and there are some good books to get.
Start developing your skill with a camera, composition, lighting etc.
Here is a great website and a youtube channel I particularly enjoy:
http://nofilmschool.com/
https://www.youtube.com/user/filmriot

And here is a highly recommended book on cinematography:
http://www.amazon.com/Cinematography-Practice-Cinematographers-Directors-Videographers/dp/0240805003/ref=cm_lmf_tit_1

Here is a book that got me seriously interested in being a Director:
http://www.amazon.com/Making-Movies-Sidney-Lumet/dp/0679756604/ref=sr_1_1?s=books&ie=UTF8&qid=1394579190&sr=1-1&keywords=sidney+lumet+making+movies