Traditional Keyframe Animation
Begin Tracing
We are going to make our trace on a separate layer, so click the New Layer button located at the bottom left of the timeline:
Use the Brush tool to trace the outline with a nice bright color (so we can see what we're doing). Don't worry, we will change to a more appropriate color when we're done:
Now zoom in and start tracing. Your keyboard shortcut to zoom in is CTRL++, and CTRL+- to zoom out: