[soamv]

This is a great question! I find that the act of explaining the problem itself helps a great deal in figuring out what the pieces are.

It's totally okay to just talk to a developer about the problem and start sketching out your ideas, without necessarily knowing the specific tasks that you're going to assign.

The abstraction level of the tasks that you should assign will also come out of the level of discussion you're able to have with the person. Everyone has different abilities/amounts of domain knowledge/available time/etc., so there is never "One True Task List" for implementing something; it must depend on the developer.

Finally, it is deeply motivating for the person who's going to do the work to be an involved part of the planning discussion. It's important to anyone to have a certain amount of autonomy in their work, and making them be a part of planning is a great way to do that.