The way I learned was to find a fairly low and a wall about the width of you hands. Start by simply jumping over the wall. Keep doing that and then start going into a pike (legs together straight out in front of you). Basically you will be in a sitting position jumping over the wall. Then start to go closer to the wall and touch it on your way over. As you get used to this you can start putting more and more weight on your hands and pushing off. Voila, a dash. From here begin changing certain things, finding what works best for you to get the most fluidity and speed out of the vault. And finally begin applying different places. Hope that helps!