I found that to get this you needed:
- a full magic bar
- a high column to jump from (one that goes to the top of the screen) or something else that will keep you off the ground
Jump from the top of that column and then float, trying to time it for maximum distance. Falling in a pit may be a trade off if you really want this achievement.
I unlocked in in level 2, but it might be easier in level 3, which has long underwater 'bubble' paths that keep you off the ground for as long as you are in them. You'll still need magic to float depending on the randomness of the level's levels platforms.