i've found that even after i have watched videos on the subject if i go back and watch them again I still pick up things i've forgotten.
As for the chin i think i've figured it out: i don't try and take it all in one pass but take several light passes to help slowly reduce it until it's gone (think of cutting the grass and lowering the mower a little each pass.) the under side is a little more difficult though since the whiskers seem to lay flat against the skin.