I want to emphasise something that is easy to overlook in a module about configuration: custom instructions are a living document, not a one-time setup.
The most effective way to develop them is to use the tool for a full working week after writing your initial instructions, and then review every edit you made to the output. Every edit is a signal. If you shortened the output three times, your length default is not strict enough. If you removed the same phrase twice, it needs to go on the avoidance list. If the tone drifted toward promotional in destination content, your tone instruction needs a more specific negative example for that context.
I review my own custom instructions at the end of each month. It takes five minutes. I add anything I have found myself correcting repeatedly, remove anything that is no longer relevant, and sharpen anything that is not being followed consistently. Over time, the instructions become remarkably precise, and the output gets closer to what I want on the first pass.
That monthly review is worth protecting in your calendar. It is five minutes that saves hours.
