ChatGPT custom instructions: build a reusable style guide for better drafts

Custom instructions work best when they are treated like a tiny editorial brief, not a place to dump every preference you have ever had.

Most people use ChatGPT custom instructions for personality. They write things like "be concise" or "act like a senior marketer" and then wonder why the output still feels generic. The problem is not the feature. The problem is that the instruction is too vague to change the model's next decision.

This workflow turns custom instructions into a reusable style guide. It is useful when you write newsletters, product pages, support docs, tutorial drafts, or internal memos and want each draft to feel like it came from the same editorial desk.

What you will build

By the end, you will have a compact instruction block that covers five things:

• What you publish and who reads it
• What the writing should feel like
• Which words, structures, and claims to avoid
• How drafts should be formatted
• What the model should ask before it writes

The goal is not to make ChatGPT "creative." The goal is to remove repeated cleanup work.

Step 1 - collect three good samples

Start with writing that already sounds like you. Pick three samples between 300 and 900 words each. They can be your own articles, product notes, emails, or documentation pages. Do not pick your most polished masterpiece. Pick normal work you would be happy to repeat.

For each sample, write a short note:

Sample 1: launch note
Audience: existing users
Tone: direct, practical, not excited
Good traits: concrete verbs, short opening, no hype
Bad traits to avoid: too many parentheticals

This does two things. First, it forces you to describe style in observable terms. Second, it prevents the model from guessing that your style is "friendly and professional," which is almost never specific enough.

Step 2 - turn style into rules

Now convert the sample notes into instruction rules. Good rules are short and testable.

Bad rule:

Write in a high-quality editorial style.

Better rule:

Open with the user's practical problem in one sentence. Avoid hype words such as revolutionary, effortless, game-changing, and unlock. Prefer concrete verbs over abstract claims.

The second version is stronger because you can inspect a draft and decide whether it followed the rule. A rule you cannot check is a mood, not an instruction.

Step 3 - write the custom instruction block

Use this structure:

I publish practical tutorials for people who use AI tools at work.
 
When drafting:
- Start with the user's concrete problem, not a broad introduction.
- Use plain English and short paragraphs.
- Prefer specific steps, commands, examples, and failure modes.
- Avoid hype words: revolutionary, unlock, effortless, game-changing, 10x.
- Do not invent statistics, benchmarks, prices, or product limits.
- If a claim may have changed recently, say that it should be checked.
 
Formatting:
- Use H2 headings for major steps.
- Use bullet lists only when they help scanning.
- Include a short checklist before the final answer.
 
Before writing, ask one clarifying question if the audience, goal, or source material is unclear.

Keep the block under roughly 200 words. The longer it gets, the more likely it is to compete with the active prompt.

Step 4 - test with a boring draft

Do not test your instructions with a dramatic creative prompt. Test with a boring task, because boring tasks reveal whether the default style has changed.

Try:

Draft a 700-word tutorial on how to organize research notes before using an AI summarizer. Include steps, common mistakes, and a short FAQ.

Then review the result against your rules. Mark each rule as pass, partial, or fail. If the model ignored a rule, rewrite that rule to be more concrete.

For example, if it still writes "unlock your productivity," change "avoid hype" to:

Never use these words or phrases: unlock, unleash, revolutionary, game-changing, effortlessly, transform your workflow.

Models handle explicit negative lists better than abstract taste notes.

Step 5 - keep project context out of custom instructions

Custom instructions are for long-lived habits. They are not the place for this week's launch, a client brief, or the exact details of one article. Put those into the active chat.

A clean split looks like this:

• Custom instructions: your writing standards
• Project prompt: the audience, source material, and goal for this draft
• Follow-up prompt: revision notes after reading the first pass

When you mix all three into custom instructions, every future chat inherits stale context.

Step 6 - make a revision prompt

Your custom instructions should reduce bad first drafts, but revision is where the style becomes consistent. Keep a reusable revision prompt:

Revise this draft against my style rules. Focus on:
1. Remove hype language.
2. Replace vague advice with concrete steps.
3. Keep paragraphs under 90 words.
4. Flag any claim that may need current verification.
5. Preserve the original meaning.

Run this after the first draft. It is easier for the model to improve a concrete draft than to satisfy every rule perfectly on the first attempt.

Quality checklist

Before saving your instruction block, check:

• It is shorter than 200 words.
• It names the audience.
• It includes at least five forbidden words or patterns.
• It says what to do when facts may be current.
• It asks the model to clarify uncertainty instead of guessing.

FAQ

Should I put every rule into custom instructions?

No. Keep permanent style rules in custom instructions and put project-specific context in the chat.

Can this replace a brand style guide?

No. Treat it as a compact operating layer that points the model toward your style guide.

Why does ChatGPT still ignore some instructions?

Long chats, conflicting prompts, and vague rules weaken custom instructions. Use short rules and repeat the important constraint in the active prompt.

Should instructions be written in first person?

It usually helps. Write them as if you are briefing an editor who will work with you every week.

How often should I update them?

Review them after every three to five serious drafts. Remove rules you never notice and keep rules that prevent repeated mistakes.