We’ve been using the following technique since shortly after Trello launched to accommodate our Kanban style agile development workflow.
Quick review: Kanban borrows from lean manufacturing principles and is a Pull based system rather than a Push based system. Team members “pull” a card into their todo list when they have a vacant space rather than having a manager or another team member “push” an item onto their todo list.
To facilitate this in Trello we did something very simple. On our board, when you pull a card onto your list, you assign yourself to the card to indicate you are working on it, when you are done, you remove yourself from the card and move it to the bottom of your current list. If you are blocked on a task but it isn’t complete, you label it with a red label which on our board means “Blocked”.
If you have an open slot on your list you look to the previous list for any cards at the bottom of the list that are not currently assigned. Unless they are blocked (red tag) they are available to be pulled.
The only list that breaks with this form is the “Up Next” or backlog list. That list is pulled from the top rather than the bottom, mostly so that we can easily visualize our top priorities that haven’t started implementation yet and can easily reorder the backlog when necessary. Same principals apply though, if the backlog has a person assigned to it, it’s not ready for development, and it it’s Red it’s blocked and can’t be moved forward. Developers skip over those cards when pulling from the up next list.
Simple and effective.