Some more from the sketchbook. I quite like a couple of the designs in this and I intend to use them in my upcoming comic at some point.
I find it's best to keep sketching until the page is filled, but if your mind tells you it's time to start, it's time to start, and one should put the sketching aside until the next time you draw. Like exercising a muscle you have to stretch beforehand, but if you stretch too much you may damage the muscle too much to make use of it when working out.
I also do my best not to erase anything when I'm sketching unless it's a doodle that I feel good about and want to extrapolate on a little more in its sketch phase. the warm-up process should be about keeping the hand fluid and letting the mind work at a free-flowing pace, not stressing over each individual scribble on the page. That's why some of these designs are half-done or just rough shapes rather than full thumbnails of ideas.
B