Go back to the Create Tab and click on the Sphere Button. Make a sphere about where the eye should go. Go back to perspective view and move the eye around till it's in place. Now chances are that it won't fit at all at first. You'll have to adjust the radius of the sphere and make it larger/smaller (most likely larger... much larger than you would think) and move it around a lot to find a way to make it fit better
So this is where I ended up. Don't worry if the eye sticks out a bit from the head in some areas. We'll be adjusting the head itself in a moment to compensate for that. When adjusting the sphere, try to get one of the sphere's pole's to be at the front-center of the eye. (see the red circles in the image above) This will make it easier to make the eye and texture it later on
Select your head model and return to the modify tab. Go to vertex mode and begin adjusting the shape of the eye so that it deforms around the eyeball better. Go back and adjust the position and size of the eyeball if you have to. Continue this until you are satisfied with the shape of the eye.
When you're satisfied with the position of the eye, duplicate the sphere for the eyeball Select it, have the move tool selected, hold down shift and click on the move arrows, but don't drag anywhere. A dialog will appear asking you to name the new object. You can if you want, it doesn't really matter at this point. Now, with the move tool still selected, go to the bottom of the screen under the timeline where the X, Y, and Z axis numbers are. Put a "-" sign in front of X if it's a positive number. If it's a negative number, remove the "-". If this doesn't move the eyeball to the other side of the face, undo it, and try changing the Z value instead.
Now the eyeball should be in the correct location, however it isn't rotated properly. Choose the rotate tool now. You will probably need to negate two of these values to get the sphere in the correct position. Try them each until you get it right.
It's a good idea to check back with the front and side references and views every now and then. Right now since we've got most all of the big things worked out, it's a good idea to just go over the entire face and fix anything that you don't like. Make adjustments to chaks, debth of eye sockets, chin, etc. Just fix anything that doesn't seem to look quite right in perspective view. Pay attention to the flow of the edge loops. Anything that doesn't seem to be flowing in a smooth curved line, could probably be changed or adjusted to work better
Once I'm satisfied with the face I move onto building the remainder of the head and neck! So that's next.
First thing I did was select the edges around the outer-edge of the face, and while holding down shift, I pulled them back, just once so that I was up against the ear. The jaw curvs inwards towards the neck so I went into vertex mode and adjusted the jaw line inwards. I created some new faces and built in a chin.
To get the mass of the back of the head, I simply created a sphere. Go into the side view, go to the Create tab and make a sphere and fit it to be the size of the head. Reduce the number of segments considerably, but make sure it's an even number when you're done. We're going to be cutting off half of this sphere and connecting it to the rest of the face. If there's too many segments it'll make it more difficult to connect the two properly
In the Modify tab, all it says in the modifier stack is "Sphere". Right click on Sphere and choose Editable Poly. Expand the Editable Poly stack and select Polygon. Select half of the sphere and Delete
Now go into vertex mode and start moving verticies around to match the face a bit better. Delete any additional faces you feel the need to. Weld Verticies together to combine them and reduce extra edges