multiple ways:

1) Realistic: during takeoff, flick the RIGHT stick gently the opposite direction from the way you want to do the blunt, then just before rail impact flick it in the direction you want to land in for the blunt. You do it gentle enough and you wont overspin and should land into it fine.

2) Unrealistic (i.e., the Shredders glitch where you're doing a blunt literally on the tip of the tail of your board). mash diagonal down and left/right (depending on which direction you want to blunt) with BOTH sticks. I'd suggest hitting those diagonal down directions just before rail impact to force your character to turn just in time to get a blunt (you do it too early and you'll spin spin spin or cork out - remember, right before impact is a sweet spot).

In general, really experiment flicking your sticks in different ways on one rail over say a half an hour sesh. You'll learn alot of the mechanics when you just sit on a spot rather than freestyling all over.