Now, I am aware there is a video on HydroSliding on here... but to me it seemed more like a... history of the sport, and not so much a guide. I have taught over 30 people how to HydroSlide in the course of my business and leisure time with the product, so I think I have a fairly good background to give you EVERY tip I have.
Now... To start of with, grip your HydroSlider by the handlebars. Place the bottom/larger foil over the edge of the dock, as seen at the 13 second mark. The bottom foil should be about 2 inches above the water, but if you are a little shorter, just under the surface MAY be okay.
Now, The pushoff is very important. You can't run before you can walk, and you can't learn to RIDE the HydroSlider before you learn to Launch the HydroSlider. Placing one foot near the stepboard, and one foot OVER THE EDGE... with the front of the foot hanging over the edge, PUSH OFF HARD with the dockbound foot. Watch how strongly the girl in the video launches. The #1 problem with learning is not launching hard enough. As you launch, place your first foot on the stepboard... and then your second foot.