I use a pretty simple idea for this: smaller the goal, futher down the totem pole I go. Think of your arm as a sectioned off totem pole. Arm at the top, elbow in the middle and wrist at the bottom. If I'm doing something in detail (small goal) I'll go to the bottom of the totem pole (wrist) If my goal is the whole form (big goal) then I'll go up the totem pole (elbow or arm, depending on size of workspace. Obivously these things can change depending on size of paper, work space, overall goals of the piece etc. But this is a good rule of thumb just to have. And then when it comes to painting its a whole different thing lol. Hope this helps!!