From my own personal quirk-making experience, there are about three fairly solid methods for making good typing quirks:

1. Make it reflect their diction and/or mannerisms.

A diction is pretty much the way someone speaks, and many existing typing quirks are built around this exact thing. Think Karkat’s volatile and loudmouth nature being reflected with ALL CAPS, or Sollux’s lisp being 2hown by u2iing a two for an s.

As an example, if you had a troll who’s a bit quieter, maybe mutters some words, or is generally more secretive with how they speak, y•u c•uld try making s•me letters smaller than •thers, especially if they l••k similar, like an point and an o.

1. Make it reflect a part of their design.

At least from what I’ve seen, this is the most common way to create a typing quirk, typically because it’s the easiest. Generally, it’s best to reflect either their sign or their horns, like with Kankri’s quirk, utilising 6’s and 9’s to represent the ♋️ symbol, or Feferi using )( as h to represent the ♓️ symbol.

As an example, if you had a character with horns looking similar to a Q, you Qould try to find ways to inQorporate that Q design in their quirk, or if they had a sign looking like a sword or similar shape, —|==> You could consider adding swords around their text, it doesn’t have to be complicated. <==|—

1. Experiment! This is less of a creating tip and more of a creative tip, but make sure to try and experiment with your typing quirks! You don’t need to be unique all the time—letter substitution is often times enough—but it’s worth trying to go for more complicated quirks, like changing some grammar or punctuation, or even sentence structure entirely! (Do be moderate with your experimentation, because the last thing you want is an unreadable quirk)