Sometimes I go to the library with a sketchpad and a bunch of nice sharp pencils and spend a few hours just making lines and shapes; sketching ideas and making notes; poring over the pictures in the nice big art books that live there. It's a wonderful way to spend an afternoon, especially on a rainy or snowy day; our library has big floor to ceiling windows, and it's the perfect place to hole up in bad weather.
Yeah, a few hours spent sketching is a really good time.
But here's the kicker: I never refer back to the sketches and notes I've made. Once I've made them, I'm done with them. And here's a secret: I've made the same sketches over and over again, I know I have. I stick with the same book for several visits, dipping in and out of a few favorites on a regular basis. My eye often goes to the same thing I sketched the last time I was there; and as I start drawing, my motor memory kicks in and I feel the lines etching their way deeper and deeper into my mind with every repetition.
When they've cut deep enough, then I can use them.