I was thinking that if someone was trying to ease someone into vaping, like an older, more reluctant individual perhaps, maybe taking teensy steps would help. The coughing thing or the thing where people seem unable to even inhale enough for vapor to come out seems to be a really common problem.
So for the first teensy step, why not just start with a low or no nic, high VG juice (as was mentioned) and have them mouth vape only? Someone on here likens it to sucking on a straw, which I think is a good analogy. Just to get the hang of it and the feel of it. Let them keep smoking analogs, and just practice the vape for fun, even better would be to find a flavor they like. You can explain that many people who vape have reported noticing more nicotine absorbtion through the mouth anyway, so ultimately, if they choose to replace analogs, they may be mouth inhaling more anyway.
Next you would work on the mouth to lung inhale. When they have that, bump up the nicotine and PG percentage a bit so they can start to get the throat hit sensation, that combines with the lung inhale may start to feel more like an analog.During all this time you can be experimenting with flavors, so perhaps you will have found some they prefer.
Only after they are comfortable with the flavor, the inhale, the device, then you can work on phasing out the analogs. I think it is really worth pointing out to the person that a willingness to experiment really seems to be correlated with a successful switch to vaping. It seems that very few people just one day grab an e cig and yee haw, forget all about analogs, would be nice if it were that easy, but these are not the same product. They are a fun (IMO) tasty nicotine delivery system, but they are not a regular tobacco cigarette, and the sensation will not be the same, and some experimentation will tell you what is the most pleasurable e cig set up for you. In the end, it is up to them to decide.....but by trying to expose them to the world of vaping, at least you know you tried.