One of the way to get a lot of horizontal speed is wavedashes. In order to perform it, you need dash, a wall and another ability. In order to perform a wavedash, you want to dash towards a wall and then hold both the opposite direction and your other ability. You don't necessary need a wall: other element like a life flower work as well. The important part is having the animation where Ori stick themself to a wall.
The further you are from the wall, the easier it will be to get the ability+direction timing but your wavedash will give more speed if you are close to the wall. It's recommended to bind the direction and your ability together in order to perform it more easily.
Regenerate
Wavedashes are most commonly performed with Regenerate because it gives the most speed.
Blaze
Another solution is to use Blaze. Blaze's wavedashes give less speed but can be used in the air while Regenerate's wavedashes can only be performed grounded.