The first Freestyle event comes in the 2-1 Beginner's Luck level in Career mode. You need to score more than 960 points to place first but you only have 1:00 to do so. If you use your SP points to buy better stunts this will increases your chances as they score more points than standard tricks though repeat tricks decrease your score. So my best advice is to stack up on level 2 tricks and possibly a level 5 trick and vary them around to make sure you do a different trick each time. Also, make sure you do a trick on a ramp which will be highlighted in green, there will be two drops during the run but I advise you not to do any tricks as you may crash (I did every single time) and this will muck up your run, just keep it simple and do a two direction combination for each ramp highlighted in green and you'll be well set for the achievement.