Now, all you have to do is go to Create>Shapes and click on "line". Start out by doing a vertical line in the middle of the face. You can do this easily just by pressing shift before you click on the other vertex. Ok, so now, keep adding vertexes along the side of the face, just like if it was a low polygon model. It's that simple. Don't make smooth vertexes. We don't want besier handles remember? You have to make only corner vertexes. This will save you from trouble latter on. Once you got the basic outline, you will notice that you have no detail for the faces profile, where the forehead, nose, lips and chin are. Therefore, you will have to refine that hole segment with additional vertexes. To do this, go to the modify panel and activate vertex sub-object. There, click refine. With the refine option active, just click on the vertical segment where you think you will need vertexes.
Be careful when placing the initial spline. It can dictate your poly count If you don't feel comfortable about it, try adding detail inside the face, and then combing with the outline.
Once you're all done, you will start by doing the content; the eyes, the mouth and so on, and so on. One thought about the surface tools. Surface tools will only fill areas limited by a maximum of 4 segments. I always like to make 3 segment areas. Pretty much like a triangulated polygon. So when your doing your contents, make sure you don't leave any hole in the spline mesh. A hole would be an area limited by 5 segments or more. Ok, click "create line", to start a different spline inside the original spline. Fell free to make the contents separate. We will connect them latter. Has the snap tool come in handy already? It's handy, isn't it? It will be a lot more.
Don't be afraid to make isolated line, it's good for reference, and you can always reposition them later.
Ok, now you're done, right? Got all the contents? Cool. To connect them together, just "create lines". If you didn't have snap tools active, you would see a different cursor when creating a line from an already placed vertex. Since snap is on, all you will see as a light blue cross. This guarantees that you will have the new vertex right in the same place as the other one that was there. Once you're done, just exit the sub object mode, and make a reference of it, to the side.
This is my final spline, and you can go and add all the additional .
Why a reference? Why not just apply the surface tools on the spline and presto! Well, I've done a lot of faces using this method, and I still forget stuff. Like, some of the faces are more that 4 sides areas... or some vertexes where badly positioned. Since I'm probably going to have to correct little bits in the model, I like to do it on the original one, so I don't have to go back and forth on the modifier stack. I know I can preview the result. But it's just a bit confusing to be working with two different things overlaying. So, reference it, and apply surface tools to the reference.
I find it easier to make a reference and change it as i go, than going up and down on the modifier stack.