My busy periods are when taking on a new project for the first time. I have to scope the work, delegate and structure the project accordingly.
Once the team has been assembled, and processes are in place, I am then busy at the start of the day where I do my daily stand ups (and deal with any impediments) that arise, and again if dragged into meetings with stakeholders discussing the project status. But other then that, if done well, everything goes smoothly, and the project starts to run itself. The team knows what to do, I then just have to periodically look at my burndown charts to see if we are on track.
During down periods, what is the best way for a project manager to use his time?