Two things help me in creating contexts. What kind of thinking do I need to do, and how long does it take me to get in/out of that mode of thinking?
I've had good results with dividing my @Computer list into contexts based on the programs I use. I find that my mindset for using a particular program can take me a few minutes to get into. Once I'm in that mode of thinking, it's productive for me to do a group of next actions that require that particular way of thinking. That spreads the switching cost out, sort of like allocating overhead to more profit centers.
For example, I do a lot of reports in QuickBooks, often exporting to Excel to further sort the data. I have an @QuickBooks context. I also use a database query program to collect and group data from our eCommerce program, so I call that @SQL.
But more important than thinking about the program to set the context is thinking about how I think when I use various programs. Some of the thinking is sequential, so I need to be in a thinking mode to follow steps 1, 2, 3, etc in precise order. The SQL query work is like that. But some work at the computer is more associative, where I'm clicking on different site links to explore various ways of conceptualizing something. That might be a context called @WebSurfing.
Those contexts require that I'm at the computer, and online. But they are more specialized subdivisions than the general @Computer and @Online contexts.
I hope that's helpful. Good questions. I'm looking forward to what others say in response to your post.
GTD Connect Team
David Allen Company