Say you are right handed, you rub from your right side to the left in a circular motion. My belly is a bit jelly like so I also grab a chunck of it and shake it as hard as I could. Its a bit painful though. But the thought of shaking as much stones out as posible and also parasites gets me excited.
Some people have great result the 1st flush and some don't, for whatever reason. Just do the best you can with the next and you might just have a great result.