It's a good tutorial, but you shouldn't depend on brushes. I lot of designers nowadays don't use brushes. Besides for the soft brush, hard brush, and pentool stroke.
You need to get the black intensity out of there; here let me show you:
You use a soft brush on whatever size you feel right. You don't go all the way black, go a little above in the color spectrum.
http://img11.imageshack.us/img11/7131/lgtfb26.png
You black out what the light shouldn't be touching, like so:
http://img27.imageshack.us/img27/5841/lgt8d69.png
Then you lower the opacity to what you see fit:
http://img196.imageshack.us/img196/7411/lgt4209.png