If an instructor is demonstrating I will generally focus on three separate things each time he does the technique.[list=1]
[*]hand - arm movement
[*]hip and shoulder movement
[/list=1] This means the teacher needs to do the technique at least three times. Most instructors show a technique 2-4 times. Sometimes you can also see the technique being done by senior students, to help you fill in the blanks.
By breaking down my observations, I find I'm able to better pick-up on what's going on, than trying to take it in all at once.
This works for me, but your mileage may vary.