Why this matters
Someone on your team types "write a LinkedIn post about our services" into ChatGPT. Back comes a post full of emojis, hashtags and words like "elevate". They spend twenty minutes rewriting it into something your firm would actually publish. Then they do it again tomorrow.
The problem is not the AI. It knows nothing about you: your voice, your rules, the services you really offer. So every person on the team re-explains the business, every time, and gets a different result.
In this module you fix that once. You build a Custom GPT: your own copy of ChatGPT that already knows your brand voice and rules. After that, a one-line request gives you a post you could send to a client.
What you’ll build
A Custom GPT that writes social posts for a small marketing agency. It has written rules (no emojis, two hashtags at most, lead with a real number) and a one-page brand-voice document it reads before it writes.
You test it the fair way: the same short prompt goes to plain ChatGPT first, then to your GPT. Plain ChatGPT gives the generic post. Your GPT gives an on-brand one you could publish.
What you need
- Nothing to start the practiceThe ChatGPT screen and the Google Drive file are practice copies inside the lesson. No account, no sign-in.
- A paid ChatGPT plan, to build it for realPlus, Team or Enterprise at chatgpt.com. Free accounts can use GPTs but cannot build them.
- Your writing rulesA short list of do and don’t. Start from the instructions file in the downloads below and change it to fit your firm.
- One brand-voice documentAny PDF or Word file that shows how you write: a style guide, a few of your best posts, or the sample guide below.
Concepts
3 ideas you’ll use in the practice.
A prompt is only as good as its context
A prompt is the message you type to the AI. A short prompt with no background gets a safe, average answer, because the AI has to guess who you are.
Give it context (who you are, who reads this, what good looks like) and the same short request gets a far better answer. A Custom GPT is a way to give that context once and keep it.
Instructions are the rules it always follows
Instructions are a block of text inside the GPT: who it is, how it writes, what it must never do. They apply to every chat, so nobody has to remember to say "no emojis" again.
Good instructions are specific. "Write professionally" does little. "Never use emojis. Use at most two hashtags, at the end" works every time.
Knowledge is the reference file it reads
Rules fit in a few lines. Examples and detail do not. That is what the Knowledge upload is for: a document the GPT can read whenever it writes, like a brand guide or a list of your services.
Only upload what you would be happy for everyone who uses the GPT to see. Never upload client files or anything confidential.
Practice
Do every step yourself in a practice copy of the real tool. It checks your work, and “Do it for me” finishes any step you get stuck on.
Do it for real
Now repeat it in your own account. Tick each step as you go.
Downloads
- Custom GPT instructions template (.txt)The exact instructions from the lesson. Swap in your own firm, services and rules.
- Sample brand-voice guide (.txt)The one-page guide the GPT reads in the lesson. Use it as a model for yours.
Quick check
3 questions to check you’ve got it.
1. Why did plain ChatGPT write a generic post full of emojis?
- It is a worse model than the Custom GPT
- It had no context about the brand, so it guessed
- The prompt had a typo
Show the answer
It had no context about the brand, so it guessed. Both use the same model. The difference is the context: your GPT has the rules and the brand guide, plain ChatGPT has only one line.
2. Where do rules like "never use emojis" belong?
- In the Instructions box
- In every prompt you type
- In the GPT’s name
Show the answer
In the Instructions box. Instructions apply to every chat with the GPT, so the rule is never forgotten.
3. Which file is safe to upload as Knowledge?
- A client’s tax return, so it can answer questions about them
- Your public brand-voice guide
- Your team’s password list
Show the answer
Your public brand-voice guide. Anyone who uses the GPT may see what it read. Keep Knowledge to material you would happily share.
AI Social Media Idea Agent
Your GPT writes great posts, but someone still has to open it, ask and copy the answer by hand. Next you build an AI agent that does the work and saves it to a spreadsheet by itself.
Start module 5 →