Think about it in terms of forcing them to react to something. One good example is running up to them and WDing in place right outside of their range. It sort of depends on how "convincing" you are, but ideally the idea should be "Well I could have ran in and grabbed/shined/upsmashed/naired, and you have to respond to me running at you somehow." If they're not reacting to you doing things like that, it generally means you could just run up and hit them.
Another really good one is empty SHing towards them. If they're committing to dash dancing and you're the one trying to be the aggressor, usually that means they're dash dancing from futher away. Landing only has 3 frames of lag, so its not exactly reactable (since you could also be DJing, or wavelanding backwards or something. This mixup game is even further explored with platforms). Because of this, you can SH towards them as a way to close the distance, and then immediately do an action like nair at them, or run up and hit them. Once again, they're forced to react somehow to what you're doing, and if you mix this in well they generally will have difficulty reacting to such an abrupt change in spacing.
edit: I'm a liar its 4 frames