By Arthur Xiao, maker of AddSpeechBubble.

• Choose a small situation: a missed train, a borrowed umbrella, or a surprise birthday cake.
• Give each speaker a different goal. One wants information; the other wants to avoid spoiling the surprise.
• Write the whole exchange as plain text first.
• Delete greetings and repeated explanations that do not advance the scene.
• Read the dialogue aloud. Change words that sound unlike the character.
• Check that the reader can tell who speaks first.
• Use invented names and clearly label the image as fiction.
• Avoid putting real phone numbers or private conversations in a public example.
• Export a readable image, then keep the text version for people who prefer it.
• If using a phone layout, try my fictional chat-image tool: free PNG, no signup, no watermark. Video export is Pro.
• If facial expressions matter, try my comic strip maker: up to six free panels.
• Final revision prompt: can the last line change the meaning of the first without explaining the joke?