I can be a bit difficult to build up speed at first. Unlike most platformers the player moves directly in the direction you hold the left stick (or in the direction of the combination of arrow keys you hold down) so if you're on a flat surface you have to hold the stick at 90 degrees to get maximum acceleration, on a steep incline you need to hold the stick to match the steepness of the incline or else you will either move away from the surface or waste some of your force pushing yourself against the surface. So on that second obstacle for example you need to start out going left, change to an upwards direction about halfway through and then go a little to the right at the top.
It's a bit unintuitive but I'm not sure how to show it better.