I guess this method of propagating a Ceropegia Woodii can be described as air layering. Even though you aren't really wounding the plant by making an incision to make it produce roots in a certain spot. Here we're taking advantage of what this plant does naturally if you don't have a lot of confidence in your ability to grow from cuttings.
All I really do is set the tuber that this vine produces in a smaller pot that is filled with soil and I bury it in a little bit. It's important that the tuber you are trying to root isn't move or gets dislocated so anchor it in. Maybe with a piece of twine or a U shaped hook you make out of a paper clip or stakes made from toothpicks. Once I have the pots in a position where I know they won't be disturbed I just start watering the smaller pot as I would the larger plant until I figure that it has started to produce it's own roots in a few weeks or months. You can tug gently on the tuber and if you feel resistance then you know that it has started to produce roots. If it lifts up and you see no roots set it back in the soil and continue to wait a little longer.
Once you have observed the formation of roots in your Ceropegia Wodii you can then snip it off from the parent plant and continue to grow it as an independent plant and transplant to a pot that is one size larger. If you find that your plant looks straggly you can fill it out by wrapping the tendrils along the surface of the pot and allow it to form tubers and root itself. This has to be the easiest way to propagate Ceropegia Woodii because you don't really have to do much once you've gotten to this point other than wait.
If you'd like to read more about this plant based on my experience growing it see this link from my Rate And Review blog.