Almost every fighter’s neutral attack combo is performed by pressing the Attack button repeatedly. During neutral attack 1, another press initiates neutral attack 2, then another press initiates neutral attack 3. For many fighters, merely holding down the Attack button executes the combo. This isn’t always desirable; most neutral attack combos are punishable if the whole thing is blocked, and the finishing attacks usually don’t have great KO or follow-up potential.
But there’s so much leniency on tapping/holding the Attack button to continue through the neutral attack combo that it can be hard not to speed through a full neutral combo. Try doing it based on timing: perform your favorite fighter’s “jab,” neutral attack 1, then wait long enough to tap Attack and get another jab, without going to the next stage in the combo. You’ll be surprised how long you can wait and still cause neutral attack 2.
The way around this is to interrupt the first neutral attack as soon as possible with something else that “breaks” the potential neutral attack combo. The best examples are crouching and shielding. You don’t have to crouch or shield long enough to see them happen as more than a flicker at best; you just need the game to register them. (As with many techniques, it can help to practice at 1/4 or 1/2 speed in Training Mode first, so it’s easier to see what’s happening at full speed.)
By cutting short the end lag of the first jab with a “flickered” shield or crouch—merely tapping down or Shield—if you then go for another neutral Attack input, you produce another starting jab. This allows you to perform earlier stages of neutral attack combos repeatedly, avoiding the unsafe finishing hits, and also sets up “tick-throw” grab attempts and mix-ups.
You can also jab-cancel by turning around: nudge the control stick to your fighter’s back during end lag of your initial neutral attacks (gently nudge rather than flick; you want to turn around, not dash in the other direction). This can be useful for some fighters like Fox, who have moves with great coverage behind. Moving in initially with a quick neutral attack can serve to hold foes momentarily and set up a solid back-hitting up tilt or up smash.