Right now for the actual modeling, I will be modeling him in polygons as I've said before there's already many good modeling lessons out their and all are slightly different. I can't explain things as well a properly trained 3d artist would, I can only just show you how I would go about my a making a head.
One of the best polygon modeling tutorials is by Dave komorowski any one learning should read it, he's a expert on his edge loops and can explain about them far better then I can. link
Right just before I start, below I've attached a picture, look at the lines i've drawn we want our polygons to follow the contours of the lines, this will make it easy to create skin wrinkles in the right places and the face expressions will deform well.
For making a head you want good references as many different facial expressions and and a front and side view if you can get them. unfortunately I have not been able to find a perfect front and side view of tom baker.
Below I've attached the reference picture I will be using, I put all the useful poses and expressions on to one picture for easy viewing, if any one reading this plan's to try making the head as well I've uploaded the full size version which you can download, 711k.
I will also be uploading the base mesh in stages up to a certain point, this is because I will be modeling unaided with no front or side pictures and will be difficult for a beginner to get the basic shape of the head.
One last thing I need to think about is, I'm trying to model a man of about 65 to 70 here and most of the pictures I am using are younger. So at the beginning I will be working off some of the older pictures and using the younger ones to make facial expression later on. It should not be to difficult I just need to capture his mad stareing eyes and smile.
For starting a head their's of course many different ways, I always start mine with a single polygon using the create polygon tool or just a simple polygon plane like below. I always start in the area around the eyes.
Here's how I start, with just a single polygon i will be working pretty quick but i will try and take a sreen shot for all the improtant actions.
Open the extrude edges menu so its aways on the screen and when extrudeing it's best to check that keep faces together is on in the menu.
I've selected both edges of the polygon then extruded both sides at the same time and scaled them out a little.
I've selected the end of both sides again and extruded them, I've started to move the points to form the shape of a eye.
Extrude both edges again.
And extrude again.
Now i use the merge edge tool to merge the two edges.
And here's our basic eye shape, the eye shape can be downloaded Here. BasePart 1 i've put them up in OBJ format if users of other 3d programs want to try.
Now select all the outer edges of the basepart and extrude all the edges at the same time.
The edges extruded.
Now I've moved the points to form the shape of the eye socket. mesh update here BasePart 2.
Now where the red spot is I have deleted the face, and where the green line is I have extruded a edge. This is because I want the polygons to follow the contours of the face and I want that line of polygons to run down the nose. Look at the picture of the man at the top of the page and your see the area I just made.
Now i've selected all the edges I have hightlighted here and then extruded them.
The edges extruded.
More 3D Graphics: 
