1. Analyze the model, Identify the Center of Interest
Your model generally has a point where it is most critical that the edges will align. For this model the eye was the center of interest. In other face models, like an alligator, the mouth would be the most important surface to model from.
The surface that is shown above used curves that have been rebuilt. Notice how the curves that are outside of the eye surface are irregular, and the curves within the eye are smooth.
The way you would rebuild curves is:
1. Edit the curve by hand as much as you can to achieve smoothness in the curve.
2. Use the Curve Edit -> Rebuild Curve -> Options function. set the rebuild type to "Uniform Knots". Key in an amount that seems reasonable for the curve. The eye surface could use 12 spans around the perimeter and 4 spans per section.
2. Create Bi-Rail Surface
Once you have the curves lined up exactly the way you want them, choose Surfaces->Bi-Rail->options. The option you want is 2+ for Gen. Curve number. Click on rebuild off for Gen. Curves (sections) and Paths (rails). Click on the number of sections you want, then click "Go". Remember, it is important what order you select the section in.
Once you have selected the sections, you select the rails, once the rails are selected, you should be able to see the surface.
3. Rebuild Surface
If you have set up your curves perfectly, you will not need to rebuild the surface. Chances are, however, that you will find for some reason that the spans in your surface are not exactly the way you would like them to be.
When this happens, the tool you would use is Surface Edit->Rebuild Surface->options. Go to the "Uniform Knots" option, click on "Change U,V", and enter in the amounts that you wanted to appear when you rebuilt the curves. You will probably want to turn off "Keep Originals" as well because the multiple surfaces tend to start getting in the way.