Hm, that’s in interesting question. Okay, here’s some things that jump to mind (in no particular order, just throwing thoughts at the wall).
What you’re parodying really makes a difference in what you can do with your parody, and that’s something to really consider. E.g. Team 4 Star’s parody of Hellsing Ultimate (which I literally was just watching a few minutes ago) can do and say a lot more, and still come across as coherent, than a parody of The Sound of Music (at least without devolving into just random sketch with parodies thrown in, ala Family Guy).
Parody (and I mean stories that are predominantly parody, not just have parody as part of their structure), tend to be significantly shorter than the works they are parodying. There’s a good reason for this (beyond good parody being pretty hard to pull of). Parody tends to build on what is already present, pulling things from the audience’s mind and turning/playing with them. Therefore less set up is naturally involved, and set up tends to be one of the easiest places to lose and audience.
E.g. You mentioned VNs, so lets take a very typical structure of a VN, the ‘harem comedy’, where a geeky guy (player stand-in at best, author at worst), meets typically five heroines. If we introduce the ‘tomboy’ character in a harem comedy, in a normal story, we show personality, mention interests, have complex interactions, ect. With a parody, we do one of those first two things, (generally the second) and that’s it. That character is now your tomboy character, no more or less.
If you start building a lot of character and complexity, that character stops being your ‘tomboy’ stand-in, and starts taking on a personality of their own. For a normal story, that’s good, but for a parody it can be bad. When that character does something, it’s now less ‘tomboy stand in does x’ and more ‘this character does x’. Hence parodies tend to just jump to the next scene, skimping on the buildup and structure of other stories.
- Parodying ‘tropes’ is pretty vague, so I’d recommend focusing in a bit. That said, parodying outside a source media can likewise be difficult, and IF isn’t really monolithic enough to have enough to parody on it’s face, without delving into the obscure. On the other hand there’s cultural parody (ala Watamote for Otaku culture and Sayonara Zetsubou for Japanese/World culture), but that’s, well, that’s really area dependent and can be pretty hit or miss.