Steve gave a great answer, just add my two cents here.
It is my first time doing glissade...the trick is you have to use your feet to shave ice/snow and let it pile under you. And even with that, depends on the snow condition (soft/wet/icy/hard), you might still go very fast.
Ice axes can be used to slow down a bit, do not count on it (maybe I didn't do it right). In my case, ice ax is like binary: either it bites into the snow and stops you completely, or it barely offers any help.
Also, pay attention to the icy surface, it might cause pretty bad skin scrape.
