There are lot's of tutorials on the web about modeling a human head, so I won't go over the merits and differences of methods again. There are a few things worse of mentioning - you will get a more successful results if you will try to model an original face with interesting features - curved nose, scars or strong ethnic elements could make your rendering interesting and believable. The best thing to do, is to look into photographic book, National Geographic magazines or other things like that for inspiration. You can scan a picture and use it as your template for modeling. I use polymodeling for my human face, it gives more control, and less trouble while rendering.
When you have your template image ready, go to Maya's front view, and in the camera attribute editor create an image plane, assign your template image to this plane.
With create polygon tool make a new polygon, which would outline the head silhouette. Use as little points as possible, and try to put them in places which would be usefull as the starting point for internal polygon edges.
Now it's time to split the first polygon vertically in the center, and then horizontally at the level of the eyebrows, eyes, and the lips. Delete the right or left side of the head (afterwards you will mirror it back, for now it's easier to work on one half) and split the remaining polygons a few times connecting them to the outer vertices.
Try to stay with a as low vertice count as possible, you will have to pull them in 3d space to get the volume of the shape. Easiest to do this is by putting another template image (at least a simple pencil sketch of the profile) into your side view, and pull the vertices into the right position. Keep your model smooth shaded, and make all your edges soft to have a better feedback of what you are doing.
It isn't as difficult as it sounds, the basic shape will appear very quickly, you might want to add some more edges here and there to get it right, but still try to keep it as simple as possible for the next step.
When you are happy with the basic shape of the head, it's time to apply a fantastic mel-script created by Dirk Bialluch
"Connect Poly Shape". It mirrors your low poly head and creates another subdivided version of the head, which makes work so much easier. You tweak a few polys and vertices of low poly half, and see the result on both sides of the smooth version. You will get a very decent result in no time.
Add detail like eyes and ears, wrinkles (the more the beter) dimples etc. Remember, some of the facial detail you can get with bump map, but the main details are better to model, rendering results will be much better. Another issue - a human face is never symetric, but the result of using the half head technique is that you've got yourself a perfectly symetrical model. So when the basic modeling is done, disconnect smoothed shape, and work on both sides separately. The more differences there will be between the sides - the more realistic the final render will appear.
Human head shading
For shading and rendering we will need other mel-scripts and plugins. The first of them - "AW goodies" is available from the Alias/Wavefront
web site, and has the tool which we will need to accomplish our task - "UV snapshot". As it's name says - it creates a UV snapshot of your model, which makes texture painting task much easyer. Just asign spherical texturing for your polygon model and make the snapshot.
If you want to get any reasonable human face rendering, you have to use big textures at least 1024 x 1024, even better twice this size, so make a snapshot of your UV's in the resolution of texture to be. Remember, maya doesn't handle very well non-square textures, especially for bump maps, so try to stay with square sizes.
If you have a good quality photo of the face you where modeling, you can use it for the texture with moderated changes to it, you will have to use some warp tools like Elstic Reality to mach your UV layout. Otherwise you can paint the texture yourself, and most of time it's much more interesting.
I always start with a bump map, it's the one which has to be re-used in other channels - specular and diffuse - the wrinkles and other features you create with bump changes physical properties of the skin etc..
Any paint program is good, I prefer Adobe Photoshop.
Create a new document in Photoshop of your chosen size, make the background layer 50% gray and load your UV snapshot as a new layer. Change this layer mode to "Screen", reduce it's opacity to 50% and lock it, so you wouldn't paint on it by accident. The rest is left for your freedom and fantasy. I use 1px brush to paint small skin detail and texture, then duplicating layer and blurring it slightly.
Usually I paint lots of small wrinkles and details arround eyes lips and nose. I also create another gray layer and add gaussian monochrome noise to it, then overlaying it on my painted wrinkles, it gives a lot of fine variations. You also make some small starlike brush for painting bigger skin pores on the nose, chin and lips.