Tips for getting AAA on Mission 42
Start by taking the higher up ones in a figure-of-eight movement. (Everything I describe below assumes you're going through the gates)
Drive up the ramp at the start, turn left, jump the small ramp and turn right to go down. Powerslide right all the way round to the right so you can go up the ramp, turn right, jump then go down the ramp to the left.
That should be all the top ones done. What to do now is powerslide left, go to the right of the ramp and hit the small jump to get the mid-air gate. Do a mid-air trick and hold left, then powerslide right across the back of the arena, so you can reach the other side and hit that small jump too. Go through that mid-air gate but don't do a trick.
Instead, do a tight powerslide to the left once you land so you'll be face to face with another jump. Do the jump through the gate and do another trick so you've got enough speed to powerslide a 180 and face the other jump. Hit that one and just drive through some of the remaining gates on the ground to get the AAA. It's difficult but once you learn the technique you just need to do it without any mistakes and you'll get it.
The important thing to remember is that you don't need to get those gates at the extreme left and right side of the arena (the ones on the ground next to the jumps). Those ones will only slow you down and you can get the AAA without them.