Pure

Stage 6 contains three freestyles, one sprint and a race. To get the achievement you must finish 1st in all five events. If you haven't already I suggest you have an atv specific to each event type (one of race, one of sprint and one for freestyle). Both the race and sprint atv's should focus on speed and handling with little recognition of tricks. While the freestyle atv should focus mainly on trick (because that's what your doing).

In the Freestyle events, make sure you focus on tricking and not your opponents or racing, I actually stop for 5 seconds at the start of the race to give myself a bit of room to move. What you want to do is build up some combo's, sometimes it's good to do a big Y or special trick and then in a previous/future jump do two/three small A jumps to hit up your multiplier to allow you for bigger benefits.

In the Race events, focus on your speed and not crashing. Be careful if you want to trick and always leave yourself enough time to plant a clean landing (which allows for a speedier exit from the ramp). Use your boost on straights and make sure not to use it before tight corners as it usually has little effect. If you know you can't win the race, then restart and hope for a cleaner run. If your still struggling try different routes and learn more about the track, it helps especially in the later stages as the shortest routes aren't often the quickest.

In the sprint events, focus on your acceleration and cutting the corners tight. Stuff away from the pack if you can as you'll get slowed down and avoid preloading over the 1-2 jumps in the map if you can as the longer you stay in the air, the more of a gap others on the ground gain.

Hope I helped and if you got any questions ask!