These are things that for me contribute to compatible touring/riding companions, learned after touring with the same mates for around 50,000km on various trips, all without any tension or disagreements.
Plan your day and ensure everyone knows the plan and is happy with it.
Similar daily distance objectives, and distance between breaks.
Similar touring speeds, which for us is usually on the speed limit
Content with similar style of overnight accommodation and happy to share
Similar budget for meals and accommodation
Stick together to help each other when it's needed
Above all, tolerant of each other's various idiosyncrasies
A total of about four bikes is my limit, and I'm happy riding on my own
Being a good pillion is something that comes with experience, and fits in with all of the above, as well as having total trust in your rider, learning when to sit still, when it's OK to shuffle around a bit, and being prepared to sleep with the rider at the end of the day.
Being a good rider for your pillion fits in with all of the above, as well as being aware of the extra life in your hands and being considerate in regard to cornering, acceleration, braking distances.