Just thought I'd mention this....I've figured out how to boost consistently off the starting line.
This works EVERY time!
Hold A the whole time it is counting down, 3, 2, 1, (keep holding A) Let's Race! Keep holding A until the words "Let's Race!" are JUST ABOUT TO DISAPPEAR, then quickly let go of A and then hold it again. WHOOSH! Off you go in a wheelie and you will wreck anyone directly in front of you in the starting line. Timing is required, but it isn't too critical and you should be able to get this down pretty quick with a couple rounds of practice.
It also seems that the longer you held A during the count down, the better the boost. So if you start holding A at 2, you will get less boost than if you were holding A before the countdown even started.
Also another tip:
If you hit the "drift" button in the middle of a jump, your character will do a little....er.....(whatever you want to call it) animation (different for each character), if you successfully complete the animation, you will boost when you hit the ground. The more animations you complete mid-air, the better the boost will be when you hit the ground.
This one seems to be more well-known, but I'll mention it anyway for those new to the game or otherwise didn't know.
Last tip:
The longer you drift, the better your boost will be.
I'm finding this game to be, in many ways, deeper than MKDS in its racing mechanics.
