Disclaimer: I suck too.
I think punishing boils down to getting the most out of each mistake your opp makes. This has a bunch of different components, and the only ones I can think of are:
1) Planning
What do you want to do with your punish. This is important to know and depends on %, position, stage, and char. This can range from kills to % to position to mind games to impressing the stream with your $vaggedge.
2) Widening your definition of a mistake
Noobs only see whiffed smashes, hard reads, and major tech errors as punishable mistakes. As people get better, that definition widens to include more and more mistakes until being a little too short with a dash dance or having a tendency to play campier after a whiffed aerial are punishable by death. If you widen your definition of a mistake, you get more punishes because they're more to punish.
3) Launching
Once you've recognized a punishable mistake, you have to follow up. The definition of a launcher as I will use the term here is a move which puts the opp into a position you can begin a combo. For example, dsmash is rarely a good launcher, but utilt often is. What moves make good launchers varies widely based on di, char, stage, and %, so there's going to have to be a lot of experimentation and study to figure out what works best. On Fox at 0% on FD, dair is awesome because you get to start the
for (percent = 0; percent <= 70; percent += 18)
{
shine(fox);
dair(fox);
}
loop. Once he's at high %, dair won't give you anything. Landing a good launcher is essential to landing a good punish, but that's a textbook on its own to figure out.
4) Extending
Once you're hit with a launcher, you should hit with extenders in order to move them to where you can hit them with another extender or a finisher. This varies hugely from char to char, but in general, shine is super good, fair is hugely undervalued imo, utilt is super good, lasers are great for forcing getups and keeping people in place, and falling aerials tend to give greater opportunity for follow-ups because you're on the ground able to do stuff earlier. I think there's a page talking about combos.
5) Finishers
The last hit of the combo. What move you pick here depends on what you want to achieve with the punish. If you want to kill them, hit them with something that'll kill them like a dair or fsmash (char specific). If you want to do damage, put them in a place where they are very likely to put themselves in another punishable situation. There are a ton of different goals you can go for with a punish and they all have different finishers and different extenders which lead into them.
I feel like in people who are good this mostly happens sub-consciously. If you think I missed something or if I am unclear about something, I can clarify or you could just tag PP or something.
