Practice is the key! I don't know, inspiration can come from everything, movies, books, songs, or even other artists... I've been drawing since I was a child and it has always been my own way to escape from reality and find my own imaginary world.
Okay, I practice a lot at school sometimes, they have an art and anime club so I'll practice there too. And inspiration can come from any where, but what inspire you the most for your art? That sound like me when I was little. Or littler any way.
Depends. Right now, I find inspiration in the tv-shows and characters I like, I imagine stories, situations in my mind about them, and try to picture them with images. Another thing that often inspires me is songs and song lyrics. I also constantly scan galleries of actors and actresses that I like, to find maybe some inspiring pictures.
It's not an equation though, there have been periods (long periods) during which I didn't feel like drawing at all, and had no inspiration... and then there are luckier moments.