My rule of thumb for Task work – and one I highly recommend Teams adopt as a part of their Team Working Agreement – is as follows: Every Team Member’s name appears on one and only one in-progress, unblocked Task at a time.
This rule does not preclude multiple Team Members from working on the same Task. It does preclude any Team Member from signing up for or attempting to work on more than one Task at time. And that’s the point. Single-item flow is the most effective, most efficient way known to develop a product.
This example (partial) task board shows the task heuristic in operation
The result of this simple rule is that no one is working on more than one Task at once, meaning no one is attempting to engage in multitasking. Another result of this simple rule is that Tasks not yet in progress are available, by virtue of the fact that they live in the To Do column on the Task Board, for any Team Member to work on, until one or more Team Members sign up for the Task. This simple visual cue helps the Team see what needs to be worked on and also helps drive cross-functional behavior on the Team by making it physically possible for anyone to sign up for any available Task.
Excerpt from The Agile Team Handbook, page 139.
All for now....