At the beginning of every race you start in the stopped position which is just standing facing the screen.
The counter goes 3, 2, 1, GO. You need to time your launch to jump from the stopped position to the forward position right as it changes to GO. So as it is counting down, right after saying "1", quickly jump and land sideways placing your right foot forward and left foot back (or left forward and right foot back). This may take a couple of races to get the timing down but it is not too hard. You will be doing a bunch of races before you are finished the game so you will have countless opportunities to try this.