Which tool to choose
Almost all AI assistants offer a place to set preferences: it's called custom instructions, profile, or assistant settings. If the AI you use has it, that's where the always-valid rules go. If you can't find it or you use several different assistants, the solution that works everywhere is a block of text saved in a note, to paste at the top of new chats. For repeated tasks it's worth creating a tailored assistant with those rules already inside.
How to do it
Consistency isn't obtained by asking for it every time: it's obtained by writing the rules once and putting them where the AI rereads them by itself on every answer.
- Decide your fixed rules: tone (formal, friendly), typical length, technical level, language, what to always avoid.
- Write them as direct, short instructions, one per line.
- Put them in the assistant's custom instructions, if they exist; otherwise in a note to paste.
- Add an example of the result you want: a short "this is good" text is worth more than ten adjectives.
- Test with two different requests and check that the tone holds on both; correct the rules that aren't respected.
The operational syntax, a block of rules to paste or save:
Fixed rules for your answers, always valid:
- cordial but direct tone, no beating around the bush
- answers under 150 words unless explicitly requested otherwise
- explain technical terms on their first occurrence
- no bullet lists unless I ask for them
- Italian, never English words where the equivalent exists
Confirm you've understood them, then answer my questions following them.
After setting the rules, make any request and check the result against the rules. If the tone is off, the problem is almost always a rule written vaguely: "be professional" says nothing, "avoid exclamations and superlatives" does.
A concrete example
Elena writes newsletters for her business and every time she fought with the AI, which gave her texts that were too enthusiastic, full of exclamation marks. She writes five rules in the custom instructions: calm tone, no exclamation marks, short sentences, one idea per paragraph, a closing without shouted calls to action. She adds an example of a paragraph she likes. From that moment every draft is born already in her tone. She no longer corrects the style by hand: she corrects only the content.
When it does NOT work (and how to fix it)
If the AI respects the rules at first and then loses them
In long conversations, instructions given out loud fade. If you've put them in the custom instructions this happens less, because they get reread on every answer. If instead you paste them by hand, repeat them in short form when you notice the drift: "remember the tone rules."
If the rules contradict each other and the result is confused
Too many rules, or conflicting rules ("be exhaustive" and "be very brief"), produce uncertain answers. Keep them few and coherent: five clear rules beat fifteen fuzzy ones. If two clash, choose which matters more and drop the other.
If you can't find where to set the custom instructions
The names and locations change (settings, profile, customization) and they move with updates. If you can't find them, don't waste time searching: keep the block of rules in a note and paste it at the top of every new chat. The result is the same, the only difference is one more copy-paste.
A tip from someone who actually uses it
The example beats the description. You can write twenty adjectives about the tone you want, but a single paragraph of "here's how it should sound" communicates more to the AI than any list. When a rule isn't respected, before adding more, try giving it an example of the right result: it's often what was missing.
Frequently asked questions
Do the custom instructions also apply to the chats I've already opened?
Usually they apply from the new answers onward, including those in open chats, but the behavior varies between assistants. When in doubt, after setting them open a new chat: there you're sure they start from the beginning.
Can I have different rules for different jobs?
Yes, and it's the best way to use them. The custom instructions set your general style; for jobs with their own rules create tailored assistants or keep separate blocks of rules in a note. One for emails, one for the website texts, one for the notes.
Does setting the style once make it rigid and impersonal?
It's the common fear, but the opposite holds: fixing the boring rules (length, no exclamations, terms explained) frees your attention for the content, which is where your judgment is needed. Consistency on style doesn't switch off the voice, it only removes the effort of rebuilding it every time.