I think it is funny that you mention the notebook idea. I am also one of the many passionate writers out there.(I am only 13) I myself have a book that i am hoping to publish (right now i am only editing) and i do keep a small journal for my book that i take EVERYWHERE. It doenst matter where i go. Any time i get a little idea or inspirations, i write it down. Sometimes it is nothing more than a single line or phrase i would like my character to say, other times a whole 2-page scene.
It really helps you stay focused and i think its kinda cool sometimes i write key words that i only know what it means and that way i can keep my thoughts to myself. Good luck!
Never Ever Stop Writing!
No matter how many rejections you get, as long as you like it, thats all that matters. And if you keep trying something is bound to come out of your efforts!