I'll give an example of Fox with a Marth above him.
If the Marth is super high in the air, you just have to follow him and wait a second before he is in range again. Or if it's not FD go to a platform and follow from there.
Now, once he is in range of your double jump, you could jump once to try to bait out a side b, double jump, or air dodge. At this point you may be able to punish that with another up air.
You could also jump in front of the Marth and stay just outside of fair range. This can bait out a fair so you can double jump and punish or land on a platform and punish, or at the very least it keeps the Marth from drifting back to center stage (if you don't have a double jump to punish with for example).
Now, when the Marth is landing and you are on the ground what you want to do is dash dance just outside of fair range. This will allow you to react to the landing and punish it, or it will force the Marth to the ledge where he is not particularly strong (or even if you're not good at dealing with a Marth on the ledge, or if it's another character, at least you have the whole stage and can pressure them in the corner).
Sometimes you can just jump up and up air them again if it's appropriate based on what tendencies they have. This works pretty well against Sheik especially because her dair is slow and pretty bad and she has terrible aerial drift.
You can jump up and quickly fast fall to a platform and use that to jump again, or shield/shield drop.
Sometimes you can waveland off the top platform to double jump and aerial to hit your opponent, although that can be pretty easy to predict.
The goal of all of this is usually to get your opponent to a decent percent and then get them off stage so you can get an edgeguard, especially against characters with worse recoveries/ledge options (with Peach it might be better to try to keep her in the air for example but idk I'm not particularly great at the Peach matchup).
For example, let's say I hit Marth with a shine at about 0 percent on battlefield. From there I'm going to wavedash out and grab, upair, fall back to the stage, double jump up air, land on a platform, up air again. Assuming no SDI, the Marth is now at like 45% and pretty high in the air. At this point, I'm going to try my hardest to bair a double jump and connect a back air. Say for example I jump once, bait out the side b, then I jump again and upair. If the Marth tries to land on the stage again I will try to either trade a back air with his fair or punish his landing with a back air, nair, or grab as appropriate (maybe even down tilt to launch and up air and KO).
Anyway that's a very specific example, and it's pretty easy to do this to Marth with enough practice. It's harder against characters like Falco who fall faster and have a more threatening downwards hitbox, but the principles remain pretty much the same. A lot of times with Falco in particular you can trade with his dair if they like to throw it out.
In general, sometimes choosing an option really quickly will work out well and sometimes waiting and punishing the opponent's option works. It all depends on the context of the situation and the players. I hope you could find something useful in all this, I realize it was a pretty long post :/
