I thought this was a well done tutorial.

I always try to do my inner-corner cuts when I've still got the knife out. (Except for when I'm feeling particularly lazy and just wing it with scissors.)

A well-made film, which all goes to show how quick and easy paper models can be built.
A suggestion from me is a part of it is already known. With success, I groove the folding lines with an old ballpoint ink out of a steel ruler.

Michael