There was a great post on the Daniel Smith website about how hard it can be to start working when you have a perfect white page in front of you. I really identified with it, especially the part about drawing on the back of crap paper and having it turn out really well. :)
I have always done better drawing on loose copy paper than in a sketchbook. Once it’s in the sketchbook, it feels permanent. If it’s really bad and it’s on copy paper, at least I can just toss it out!