One of the simple things to forget is when to draw what you're going to whittle, on the piece of wood. I, more than often, just pick up a piece of wood and immediately draw what I want to whittle.
A better way to start is to make your initial knife cuts into the wood, to rough out the general shape, before drawing on the wood. When whittling a face, it's the features that will make the final piece, what it is. Before drawing the features, rough out the head tilt, left or right, back or forward. If there's a hat, rough it out. Only after you have roughed out the face, should you draw in the details to be carved. When you do this, you don't carve off the drawing before you can use it to carve in the details/features.