In Xbox Live, you must select the Hardcore game mode under Pro Tour. These races are named "hardcore" because there is no HUD, and no assists. Typically the big Dirt fans prosper in this game mode, so you may have a hard time winning. Try finding a game with only a few people (3 or 4), and increase your chances at winning. The track and discipline will be selected automatically, so there is no way to make the races go faster. Just keep at it, and go for that win. Once you come in first, the achievement will unlock.