As with pincurls, so with waves... According to this article, ribboning and stretching the hair should be done for pincurls AND fingerwaves. However, please note: stretching ("ribboning") wet hair on a regular basis will damage your hair. If you plan on doing this often, skip the stretching, and just make sure that the hair is smooth and flat. Works almost as well, and won't damage your hair.

Hair should aways be "ribboned" before forming into curls. Hold the strand between your thumb and index finger, as shown. Then run comb through to the end of the hair. Strand is held between thumb and index finger of left hand.

Then while holding strand with your left hand, use your right thumb and index finger to run through the hair strand, exerting pressure as you go along. For best results in forming curl, this should be repeated two or three times on each hair strand.

In the formation of waves, the stretching influence can be introduced by combing through the hair firmly with the fine end of the comb. As comb moves through the hair, all of the top side of it should press against the hair, causing pull or stretch.

As mentioned before, the comb must pass entirely through the hair to the scalp when forming fingerwaves.

Compare this method of forming waves with that shown. This is the average way of making waves, with no stretch or pull exerted on the hair. In this method, comb is held loosely and up, rather than pressed against the hair.

Note in this picture that they are forming the two dimensional waves. Rather than pinching the wave, each wave formed is held in place with a finger pressed very tightly against the head.