This is by far the hardest achievement in the game. First of all you have to get a good jump, which means guessing. There's really no warning as to when the gun will go off, you just have to take a shot. There's no penalty for going early, you just have to start over. Also if you're not on the inside, don't even bother, I don't think it can be done.
So get off the line with a 90 plus, and mash the a button super fast. You have to play the first turn really well, so ideally you only hold down the trigger once, and let go once, (that means starting your turn a little later than you think, which also lets you mash the a button a little longer). Once turn one is done you should be significantly ahead of the pack. I hold left on the left stick the entire race, which, if this achievement takes you as long as it took me, will be exhausting. This way if your turn is too wide, you steer back to the inside on the straight away and cut down distance. It also helps on cornering.
From there you just have to hit basically all green footsteps. When I got it, I think I got one red and one yellow, but they were late in the event. Sometimes it's tough to tell if the first step will count out of a corner, but just try to hit them all even when they don't count to be safe. Some straight-aways give you 4 steps, others you can squeeze in a 5th. It's rare that you have to take 5 steps, but the 5th helps make up for a red or yellow step. If your meter is already full, I don't think it adds speed. Corners must be sharp, but if you cut it too close and cross the line, you'll be penalized with a slowdown, and it's over.
The race counts backwards from 15 laps, but you only have until the end of lap 5 to lap the last place skater. As soon as you pull ahead, the event ends.