It's pretty easy to do three or four if you can curl the left and right side of your tong---kinda like a u---you start out with your tong pretty close to flat in your mouth and don't blow the first ring out far---just about three or four inches in front of your face---then curl the edges of your tong up a tad and blow the next ring with about the same amount of force---curl you tong up more---and blow a little harder now to compensate for the distance the rings have made from you---and so on.
I can also bounce smoke rings off of bar tops and trap them in beer glasses.