do it as ryan described but i have found success with pumping the gills closed while stripping which makes them come out quickly.
i use a tooth pick with the sharp end broken off, hold the fish in your hand with its head between your thumb & index finger & tail toward your wrist. open her mouth with tooth pick in the other hand then gently but quickly squeeze the gills closed & repeat the squeezing until empty. some fish are better than others to strip, my yellow females are so easy, the last time i got about 45 fry from 6 squeezes.
my red zeb female fights for every fry so she is much harder to strip & the baenschi freaks out the moment you put her in a net & spits em stright away. only problem with that is you have to net her almost straight away or she will spit in whatever tank she is in.