You can do just like LadyKylin said. Though I like sketching straight on paper cos it's more "free" to me and looks a bit different than work where I pay attention to pencil lines. But as you see those aren't full drawings, with no eraser I make anatomy and proportion mistakes which I cannot correct. For bigger things I sketch by pencil first..
Thanks! I really enjoy drawing without erasing, it's more 'free' to me and looks different than where I have to pay attention to my pencil sketch. But that kind of thing is good for simple sketches (I usually make mistakes when I try to draw full figure).