Okay, from what I learned, here's how. Do this and sonic will spin dash for a few
seconds:
At the start of the level:
1: when the countdown starts, get ready.
2: at "go", hit the boost button
During the stage:
1: look for a dash panel
2: boost when you go on the panel

hope this helped.

Oh, I think I just realized what you meant, just start moving in a direction and double
tap the control stick in the direction you're going to dash

hope this helps

For werehog:

Quickly flick the numchuck twice in the direction youre going.

For sonic:

To do a starting dash, after the countdown reaches 1 at the beginning shake the wii remote
forwards, just to say the starting dash does give you a few rings if you do it
succsesfully.

To do a dash while running, simply shake the wii remote forward.

Enjoy