I know that one of our old students took the Paramis and decided to work on one each week over a period of 10 weeks, and they found it every useful. By focusing on one particular Parami they were able to ask themselves, "How can I develop this particular Parami as much as I can this week?" I shared this with one of our other students and by the end of the week his daughter was joining him in the project. So this was very helpful. By focusing on one Parami we may see opportunities we didn't see previously.
However, at other times throughout the day, different situations show us particular Paramis that need to be worked on. So it's both really. At times we may decide to focus on a particular Parami, just as we do with the special Mindfulness activities, and try to develop it to a higher level. At other times it's more free flow, that is, we're trying to see the situation and which Parami tend to be the most important at that time.