When I sit down and draw I don't just throw myself into a final piece. Like any excercise its good to stretch out the muscles before using them, so I usually spend 20mins or so warming up by doodling. I love doodling, there are no rules, no mistakes, no wrongs and no failings. Just the beauty of making marks on the paper for my enjoyment. Some times it leads somewhere new, sometimes it doesn't, but it's always worth it.