Process

• Include direct URL of product if possible.
• Write a small summary describing the feature.
• Chart the happy-path and describe it. Flowchart if too complex.
• List documents related to feature. Specify document page and additional references if necessary. If the document is in a Trello card, link the card on this new one to avoid duplication.
• Create a checklist and add as many items as possible as you think about the requirements of the feature (be broad here, make sure not to forget things that might seem obvious).
• List permissions or user roles necessary to accomplish card. Describe them.
• Think about default values for data. Describe them.
• Think about error cases, include as checklists and define what to do if they happen. Examples of error cases: missing input, wrong input, missing data, duplicate data, missing permissions, going directly to a later step of a flow, offline user.
• Think about edge cases related to side effects, include as checklists and define what to do when they happen. Are edge cases related? (For example, considering the feature "As a free user, I can become a premium user by paying a subscription plan with a credit card", an edge case is when the user pays but afterwards asks for a refund directly to his credit card operator. An appropriate response to this situation is having some sort of webhook on the application to get notified when an user cancels a payment.)
• Think what messages and other feedback the user will see. Describe them. Include the copy (texts).
• Include ideas and tips on implementation details. Example of tips: libraries and tools to use, debugging tips, performance bottlenecks, modularization tips, database modeling, code organization, data formats to use, etc.