I have a board called Ideas for collecting. Usually I just put the thought in the card title.
From there more details can be added in the description, and eventually the card can be moved into its own list or board for further expansion.
Since I'm on Android, I have the Add Card shortcut on my home screen, which means there's very little friction to adding new ideas.
- Google Keep for quickly jotting down new ideas on the go (usually just a line or two so I can remember). This is my temporary record.
- Then, when I have time at the end of day, I add to to my document in Google Drive with more details, description, etc. This is my permanent record.
- When I'm ready to work on something, I add it to Trello with specific tasks, deadlines and reminders. This is my task manager.
One thing I'm failing to consistently do is to revisit old ideas periodically and remove the old ones I no longer deem worthy exploring.