It's easier with N > 2 people involved but the rough workflow goes:
a) create a story in Pivotal that covers a new use case or a tweak to an existing one
b) start the story, work on the use case, add notes at the end of working on it so next time you work on it you can reference them
c) when you finish it, mark it 'finished', then deploy it and mark it 'delivered'
d) Then do acceptance testing: ideally automated, but manual is fine too for most cases. This is where it's nice to have a 2nd person check it for you. If it works, approve it, if not, reject it and go back to work.
Also, if you're not using unit tests, they're really helpful to keep you on track - never walk away with passing unit tests, and you always have something to start with next time you go to work.