Just wanted to add some tips onto Skill's solution.
There are two races and two sprints in Stage 1 and for this achievement you need to place 1st in all of them.
Regarding the sprints, your atv should be focused on acceleration over top speed due to the shortness of the laps. Take the quickest routes with the least jumps and don't preload unless you have to. That goes to say that you shouldn't trick either.
Races are similar, but a bit different. You should have your acceleration and top speed about level or balanced (I prefer Top speed a bit higher). Strictly focus on the racing part of the game, take the routes you think are quickest with the least jumps and don't preload unless you need to. I would say don't trick unless you come up to a big jump, you can trick w/o the loss of speed, etc and you get a little handy boost.