Most sculpting or speed-sculpting in ZBrush starts with loading a Sphere as a tool. For organic shapes such as a head, the round shape gives a good starting point.
The Sphere has a high subdivision from the beginning. In order for greater control over the mesh, hit reconstruct subdivision 2 times.
I find it much easier to work with a model on these levels before going up, plus the high polygon count the Sphere has initially takes more computer-power to calculate.
It all depends on what you want to do, but remember to take advantage of each SD Level before moving up the next.
First make sure you have the Sphere centered and that you are using the Move Brush with a suitably large size and not to much pressure. Somewhere between 20 - 50 is a good starting point.
Press X to make sure you get mirrored deformation as you sculpt. You will now see 2 red dots indicating you are in X mirroring mode.
Now by click-and drag, shape the Sphere into the basic shape you want. Remember to keep rotating it and sculpt from all angles, it´s real easy to end up with a model looking great from 2 angles but horrible from the third.
As you progress further, turn on Polyframe so you really get a good look at the mesh and edge-flow. This is a great help on lower SD Levels but can be a complete pain higher up.
When the model is starting to get the overall shape and silhouette you are after, go up the SD Levels and begin to refine it by using Standard and Clay Brush.
Add to the volume or reduce to make eyesockets by CTR-clicking and smoothing by holding down the Shift-key.
To get greater control, you can mask of the area you want to modify by holding down the ALT-key, and then painting the mask onto the model. This is a great way to get small details right.
When you are finished continue to add in details until you are satisfied. If you want to animate the model or correct the edgeflow you need to retopologise it.
I´ll do some retopologising in the next tutorial.
I hope you found this tutorial helpful.