I'm learning how to do this myself, and so far I'm having lots of luck with holding vapor in the back of my mouth and
throat, making sure my tongue is out of the way (holding it down), and with a somewhat "o" shape with my lips, make a very tiny mini-cough type motion in my
throat. This description may be fairly unhelpful, lol. Also need to make sure there's no air disturbance around you (fan, open window, cats running around, etc.) and don't blow air out of your nose. So far mine aren't as robust as the picture you posted, but they're definitely vapor rings (new cereal name? heck yeah).