watch cyclocross dismount vid on youtube. don't do it any faster then you can run, or you will be dragging knees. I witnessed a friend do it at the front of the pack on lap one. He got the simpson's laugh and point from me

tips:
have mtb shoes
quick release pedals, aka Crank Bro egg beaters or Candys

Two styles:
cowboy dismount
swing unclipped leg between clipped in leg and frame. Start to run while braking with BOTH hands, Lets you dismount and run in stride just make sure you click your clipped in heal out fast and HARD. Timing is key, if done right you can run in stride, aka faster speeds than cowboy.

Practice in grass!!! It mount, don't jump on your junk or bib padding. Aim to put the saddle high on the inside thigh and then roll onto the saddle.