try this: get into whatever sw you want, and fall to the bottom of the level (preferably pick one where the bottom of the level is close to the actual boundaries. pick any piece of scenery to look at, as long as it has some horizontal edge on it. look at it and hold l. you may have to wait a bit, but samus should start vibrating up and down at some point (you'll notice because the horizontal edge is shaking). that's when you're allowed to jump
are you already refering to aether jumping? because my current main concern is even knowing when I'm in the aether, since I haven't even been able to float : /
well that refers to jumping when you are not in the aether. if the screen shakes like i just described, then you aren't in the aether. what i usually do is mash the jump button until samus jumps (it doesn't happen every time you press it), and then move away from the stage. if you stop ascending/descending mid jump, that means you are in the aether.