Well, if you go and look at your avatars, almost all of them still have non-erased pieces around the actual picture itself. What I usually do to help is this:
1: Make a "Background" layer, and paint-bucket it black.
2: Then, I add the picture in question as a forward layer, and use the black layer as a guide.
3: When i want to check how I am doing, I simply turn off the black layer, that way I can see what still needs to be done.
Note: Be sure to always have your picture on transparent when creating it. That way, when you turn off the background layer, you can see more clearly what still needs to be done.