Expanding a little on what Drevin Knight posted, this also includes the first nine moves leading up to the section he described. Rather than learn the pattern from a video or memorize the whole pattern in advance, just do them in sets of three to five, pause, look at the next three to five moves, un-pause and do them, pause again, and so forth. To make it a little easier, I've spaced them out in sets of 4 moves.
You will move Deadpool to this location in the tube, as indicated by the list. Doing this will let him pass through the gap in the grating and avoid damage for the entire ride.
L = Left
R = Right
M = Middle
The full solution is:
R L R L - L R L M - R L R R - R M R R - L M R R - L R L
For completeness, you get this achievement at the end of the tub slide in the chapter "Taking a Chance". This happens after the fight with Arclight, after the section with Vertigo and the switches, shortly after encountering Vertigo again. You'll drop into the tube and begin sliding forward. This is where the pattern above will begin. Simply move to either side or in the middle, as indicated, and after you pass by a grate, move to the next position in preparation to pass by the next grate. For positions that repeat, just stay there for additional grate(s) for that move.
The achievement unlocks at the end of the ride, when Deadpool smashes up against the end of the tube.
If you fail, pause and restart the checkpoint. This does not void the achievement as is the case with some of the others.