I usually use my artbooks for random drawings but mostly for figures like anime-style or chibi. Sometimes they turn out good, sometimes not. I used one for collage but am saving the others for watercolors since watercolor paper/books are expensive over here.
I guess the type of paper or artbook i draw or paint on depends on the medium I use. For normal painting with pastels, I usually use the cheap school artbooks. The pastels are super good and have a glossy shiny after sometime so the paper or fixatives doesn't matter. For acrylics, I use canvases and normal tiny chibi pencil sketches or ideas, I just use my diary.
I suppose in your case, you can try and experiment. Like use your first sketchbook to draw and paint and scribble all kinds of things. That's what I do with my diary. When I get ideas, I sketch them out to transform it later on my artbooks. But don't be afraid to get your sketchbook messy too! It's the process of learning. Like, I drew a lot when I was a kid. Mostly from my imagination, anime-inspiration and art class. But when I like compare my drawings, I can see the improvement and my level of creativity. I also jot down random ideas or stuff that I find interesting around me as well. Sometimes, I take photos.
What I'm saying is, explore. draw a lot even if it's rough ones. Somewhere along the way, you might make a masterpiece! =D And once you are done with your first sketchbbok, you'll probably get an idea of what you want to do with your next one. Just don't jump into a new sketchbook when you are halfway throught ur first! And NEVER rip crappy or 'wrong' pieces either. That's my art teacher's words to you. =)
Don't think it helps you much but I hope you get some sorta inspiration. =)