Face the inside wall of the chute as you go down it.
You should be almost touching the inside wall of the chute as you exit it.
As you exit, quickly switch the direction you are pointing so that you hit the ramp
straight-on, launching perfectly vertical. Gain horizontal speed while airborne by
accelerating in the air, trying to approach the far wall by the time you hit the
descent.
Try to crouch for as little time as possible as you go under the barriers. Tapping
the crouch key and letting go immediately is enough. Try to make your turns (flicks)
as you are
going under the barriers, because you can't accelerate while you are crouching anyways.
Also, keep pressing forward and sprint while you are crouching under the barriers,
otherwise your stamina will drain very quickly. You should
read this information regarding the crouch.