The first step is to define the skill, ability or limitation that you want to model, and the context in which it occurs. Chunking this down to a reasonable size is very important, particularly when you have limited time. Even when you have more time it is usually much more useful to chunk down to components, model each one separately, and then integrate these components into a larger model.
One important distinction is between modeling a process that is mostly internal, such as shame or feeling bad about being criticized, in contrast to processes that are interactional, such as negotiation or teaching. Negotiation or teaching is inherently more complex, because you have at least two individual worlds and their interaction to deal with.
It can be useful to chunk down to a particular kind of interaction, or stage in the interaction, or even to one person's process/response in the particular interaction.
A precise model of a small part of a process is generally much more useful than an imprecise model of a larger process—and you can build a precise model of a larger process by modeling small pieces of it and then integrating them.
There are many possibilities for how to choose a starting point. Following are a few of the possibilities that we have found useful: