fill your mouth with smoke, then close your mouth and push the smoke out without actually blowing it out, while you do that be steadily inhaling through your nose...
I'll get a picture of my hookah up here when i get back to school.
some tips...
1: break your coals at least in half, and place the pieces on the rim of the bowl, not in the middle. coals should never be in the middle, it leads to harsh smoke from too much heat.
2: use less tobacco than you think you need, everyone overpacks their bowls.
3: don't start pulling until your coals are fully lit, you don't want that nasty shit in your shisha or in your lungs.