Well, it sounds to me like you already know how to ask. It isn't easy, but all oneneeds to do is open their mouth and ask... right? There are two problems (for me, too: getting up the courage to ask a total stranger, and "closing the deal". To gain courage and confidence I started with "safe" options - like my kids who wouldn't dare to say no. Well, they might, but it is more likely that they'd say OK and be fidgetty, distracted, and goofy to encourage me to cancel the session. But sometimes they comply and it turns out the work for both of us. Fewer words are better. I often show them the camera and grunt something that can be interpreted as "sit... now". Next step is someone who might be a bit less compliant - wife, mother and mother-in-law in my case. Similar techniqe can be applied but much more grief is likely to result. Once past that phase, asking total strangers should be easier. "Closing the deal" isn't as easy. I try to remedy that by having a camera in hand and ready to go.. NOW. Assuring them that they look great just as they are goes a long way, whether it is really truthful or not. Once that has been accomplished it is a lot easier to start discussing clothing/location/posing/lighting changes. Begging doesn't work well for me - if they say no twice it is time to move on and try again later. Good luck!